Waste paper-based carbon foam capable of being used for interface light evaporation seawater desalination and preparation method and application of waste paper-based carbon foam

Abstract

The invention belongs to the technical field of solar seawater desalination, and particularly relates to waste paper-based carbon foam for interface light evaporation seawater desalination as well as a preparation method and application of the waste paper-based carbon foam. The preparation method provided by the invention comprises the following steps: a) cutting paper wastes into fragments, and then grinding to obtain paper powder; b) mixing and grinding manganese acetate tetrahydrate, iron nitrate nonahydrate and citric acid monohydrate to obtain manganese-iron-citric acid slurry; the step a) and the step b) are not limited in sequence; c) mixing the paper powder and the manganese-iron-citric acid slurry, and then uniformly kneading and molding to obtain a carbon foam precursor; d) calcining the carbon foam precursor under a limited oxygen condition to obtain the waste paper-based carbon foamate.The preparation method is economical, simple, safe and environmentally friendly, the prepared carbon foam material can efficiently convert solar energy into heat energy and localize the heat energy on a gas-liquid interface, and efficient and continuous evaporation of water molecules at an evaporation interface is achieved.

Description

Technical Field

[0001] This invention belongs to the field of solar seawater desalination technology, and specifically relates to a waste paper-based carbon foam that can be used for interfacial photoevaporation seawater desalination, its preparation method, and its application. Background Technology

[0002] Seawater desalination is one of the most effective methods to solve the problem of freshwater scarcity. Traditional seawater desalination technologies fall into two categories: thermal desalination, represented by low-temperature multi-effect and multi-stage flash evaporation, and reverse osmosis membrane desalination. Both technologies consume large amounts of high-grade energy, such as heat or electricity, inevitably exacerbating the greenhouse effect and environmental pollution.

[0003] Interfacial solar steam generation (ISSG)-based seawater desalination technology utilizes the design of photothermal conversion materials and effective optical and thermal control to fully absorb solar energy and localize it at the gas-liquid interface. This targeted heating of the thin-film water at the interface generates steam at a temperature far below the boiling point of water for seawater desalination. ISSG's energy source is solely solar energy, and it can achieve a photothermal-to-steam conversion efficiency exceeding 80%, making it a promising approach for innovative seawater desalination technology in the context of dual-carbon energy.

[0004] The core of the interfacial photothermal evaporation seawater desalination system is the photothermal conversion material. Carbon is the most abundant element on Earth, and carbon atoms undergo sp... 2 Hybridization can form a six-membered aromatic ring and a π-bonded conjugated structure, while π electrons can be excited by almost all wavelengths in the solar spectrum, resulting in π-π hybridization. * Leap; when π * When electrons fall back to the ground state, they cause lattice relaxation, which macroscopically manifests as a temperature increase. Carbon materials have stable absorption capabilities throughout the solar spectrum. They are abundant in raw materials, inexpensive, highly stable, and environmentally friendly, making them suitable for technological transformation and widely recognized as the most promising photothermal conversion materials for practical applications.

[0005] Carbon foam is a unique type of porous carbon material with a continuous three-dimensional cross-linked network structure. It possesses characteristics such as low density, high porosity, low thermal conductivity, and high chemical stability. The porous structure of carbon foam reduces light reflection and increases optical path, thereby effectively enhancing light absorption. It also serves as a channel for moisture transport and vapor escape. Its low thermal conductivity effectively localizes the generated heat at the water-air interface, reducing heat loss. Therefore, carbon foam is a highly promising interfacial photoevaporation material.

[0006] Coal tar pitch is a typical raw material for carbon foam. Scientific literature (Journal of Beijing Institute of Technology, 2012, 32, 641-644) used AR mesophase pitch as raw material to study the effects of nucleation temperature, initial pressure, and curing temperature on the pore size and open porosity of carbon foam. The carbon foam preparation process employed relied on a high-pressure reactor and precise temperature control, resulting in high equipment costs and complex operation; the high-temperature and high-pressure environment posed a risk of leakage or explosion; and the small molecule gases (such as alkanes and aromatic compounds) generated by pitch cracking required strict sealing, posing an environmental pollution risk. Scientific literature (Functional Materials, 2010, 41, 1552-1560) prepared carbon foam within a foaming temperature range of 390~450℃, studying the effects of temperature on pore structure and thermal conductivity. The carbon foam preparation process employed involves a high-pressure reactor (initial pressure 3 MPa, final pressure 10 MPa) and high temperature (450℃), requiring equipment that is pressure and temperature resistant. The coordinated control of pressure and temperature is challenging, and high-temperature, high-pressure operation is prone to safety accidents. While nitrogen protection reduces oxidation risk, improper handling of asphalt cracking gases (such as polycyclic aromatic hydrocarbons) can pollute the environment. Scientific literature (Carbon Technology, 2013, 32, 1-4) reveals through differential thermal analysis and electron microscopy that low-softening-point asphalt forms regular spherical pores through homogeneous nucleation, while high-softening-point asphalt and coal form irregular pores through heterogeneous nucleation. The carbon foam preparation process uses a high-temperature, high-pressure reactor (500℃ / nitrogen pressurization), which presents problems of high equipment cost and high-pressure operation risks. Precise temperature gradient control is required for raw material pretreatment, increasing operational complexity. The pyrolysis of coal tar pitch produces sulfur-containing volatiles, posing an environmental pollution risk, and the entire process relies on inert gas protection, resulting in high production costs. Scientific literature (New Carbon Materials, 2006, 21, 193-201) describes the preparation of carbon foam via pressure foaming, emphasizing the influence of uniform temperature field and pressure on pore structure. The carbon foam preparation process employed requires staged isothermal control at 330-550℃ (total time >5h), with graphitization reaching 2800℃, resulting in extremely high energy consumption. Multi-stage heating and pressure control (3-10MPa) place stringent demands on equipment precision and have low operational tolerance. High-temperature graphitization requires continuous argon protection, leading to high gas consumption and significant carbon emissions, resulting in a heavy environmental burden. Patent (CN115072699B) proposes using coal-based soft pitch as raw material, modified by vacuum distillation, air oxidation / thermal polymerization, followed by low-pressure foaming. Vacuum distillation (200~300℃ / 0.01~0.09MPa vacuum) involves high equipment maintenance costs; oxidation modification requires 4~8 hours of high-temperature treatment (280~350℃), resulting in high energy consumption and the generation of organic waste gas; although the pressure is reduced in the foaming stage (2~4MPa), the process is prolonged due to multiple crushing, compaction, and segmented carbonization (1000~1200℃), increasing production costs, and the use of organic solvents (such as tetrahydrofuran) poses safety risks. Patent application (CN119591104A) describes the preparation of foamed carbon by impregnating coal liquefaction pitch with polyurethane as a template.Pretreatment requires concentrated alkali etching (10~15% KOH, 40~70℃), generating alkaline wastewater; repeated impregnation-extrusion operations rely on manual labor, making continuous production difficult; the carbonization activation stage (500~900℃) requires steam, resulting in high energy consumption and sulfur-containing flue gas, necessitating tail gas treatment facilities and incurring high environmental risk control costs. Patent application (CN118579755A) uses heat treatment to modify mesophase pitch, preparing high thermal conductivity foamed carbon through self-foaming. Pretreatment requires a high-temperature, high-pressure reactor (300~400℃ / self-pressurization), resulting in large equipment investment; the post-modification foaming temperature of 500℃ combined with high-pressure nitrogen (4~6MPa) presents high operational risks; the graphitization stage requires ultra-high temperatures of 2800℃ (argon protection / gradient heating), leading to high energy consumption and poor economic efficiency.

[0007] Coal is also a relatively common raw material for carbon foam. The patent (CN102849723B) describes a process where bituminous coal is pulverized and then enriched with vitrinite using zinc chloride or benzene-carbon tetrachloride flotation solution. This is followed by high-pressure nitriding (0-10 MPa) at 470-530℃ for foaming, carbonization, and graphitization at 2500-3000℃ to produce graphitized carbon foam. This process consumes large amounts of flotation solution and inert gas, and the high-pressure autoclave and graphitization furnace equipment are expensive. Furthermore, the flotation steps require multiple water washing and filtration processes, resulting in high energy consumption. The centrifugal separation and high-pressure foaming steps are cumbersome, requiring precise pressure control and demanding high operational skills. Benzene and carbon tetrachloride flotation solutions are toxic and volatile, easily leading to chemical exposure. Residual flotation solution and organic solvent waste may pollute water and soil, requiring strict treatment. Additionally, the high-temperature graphitization process consumes a large amount of energy, increasing carbon emissions. Patent application (CN117637355A) uses coking coal, bituminous coal, and vitrinite concentrates of coking coal as raw materials, adds carbon black or expanded graphite, and produces activated carbon foam with a micron-nano scale biporous structure through high-pressure pyrolysis, carbonization, and KOH activation, for use as electrodes in supercapacitors. This process involves large investments in high-pressure pyrolysis equipment and high consumption of KOH activator; the nitrogen purging and depressurization operations of the high-pressure reactor are complex, and KOH impregnation requires ultrasonic treatment and hydrochloric acid washing, making the process cumbersome; safety hazards include high pressure risks, potential corrosion accidents caused by strong alkali and acid treatments; if KOH and hydrochloric acid waste liquids are not neutralized, they may pollute water bodies, and the activation process releases harmful gases, requiring compliant waste management. Scientific literature (Journal of Inorganic Materials, 2016, 31, 961-968) uses vitrinite concentrate from coking coal as a precursor and analyzes the effects of foaming temperature, pressure, and time on pore density, pore size distribution, and average diameter using a high-pressure nitriding method (combined with the nucleation theory of microporous plastics). The drawbacks of this process are: parameter control relies on experience, the depressurization rate and isothermal time require precise control, and the operational error tolerance is low; high-pressure experiments carry the risk of equipment explosion, and contact with zinc chloride flotation solution may cause skin irritation; untreated flotation solution residues and pyrolysis volatiles may pollute the air, and insufficient waste recycling increases the environmental burden.

[0008] Carbonized phenolic resin can also produce carbon foam. Patent (CN100453458C) uses thermoplastic phenolic resin as a base material, preparing a precursor through pressurized foaming and curing in an autoclave, followed by high-temperature carbonization to obtain foamed carbon. This process requires high-temperature, high-pressure equipment and high-purity nitrogen protection, resulting in high energy consumption and significant equipment investment. The autoclave depressurization rate needs precise control, making operation complex and susceptible to pressure fluctuations. Safety risks include high-pressure explosions and the potential release of toxic gases from the decomposition of the foaming agent (NH4Cl). Environmental risks involve the volatilization of organic solvents (ethanol, propanol) and nitrogen emissions, potentially causing air pollution. Patent (CN116621581B) utilizes sunflower stalk pith nanoparticles as a foaming agent, preparing nanoparticles through steam explosion and acid hydrolysis, and then combining this with microwave heating to achieve atmospheric pressure self-foaming. The process involves straw pretreatment requiring steam explosion and acid hydrolysis, which involves complex equipment and difficult acid recovery. Preparation relies on precise control of stirring rate and microwave power, resulting in poor process stability. Microwave heating may cause localized overheating leading to resin degradation, and the acid hydrolysis process poses a corrosion risk. Acid hydrolysis wastewater (containing sulfuric acid) and straw treatment wastewater require strict treatment to prevent soil and water acidification. Scientific literature (Solid Rocket Technology, 2014, 37, 113-117) introduces phenolic hollow microspheres into resin, followed by molding and high-temperature curing to obtain the precursor. This process uses imported hollow microspheres as raw materials, resulting in high raw material costs. Molding requires static setting and long curing times, leading to low efficiency and difficulty in large-scale production. High-temperature curing may release volatile organic compounds such as formaldehyde, requiring treatment of volatile organic compound emissions.

[0009] In addition to the aforementioned fossil and synthetic raw materials, biomass is also used as a green and low-carbon raw material for charcoal foam. Patent (CN115043388B) describes the process of cutting yam into specific three-dimensional structures, followed by freeze-drying and carbonization to produce charcoal foam. When applied to seawater evaporators, the resulting material achieves an evaporation rate of 1.7~2.4 kg / m³. 2 However, this process employs freeze-drying and vacuum carbonization, which involves expensive equipment and high energy consumption, resulting in high production costs. Furthermore, it requires precise control of the yam block height and drying time, making the operation cumbersome and susceptible to the properties of the raw materials. Patent (CN114618549B) uses starch-based raw materials as precursors, combined with yeast fermentation and microencapsulation activators, to produce carbon foam through fermentation, cooking, microwave drying, and segmented carbonization. This process requires significant investment in microencapsulation activators and constant temperature and humidity fermentation equipment; microencapsulation residues and post-carbonization washing wastewater require multiple boiling treatments, potentially causing secondary pollution, and the starch raw material may create competition in the food chain.

[0010] In summary, the existing carbon foam preparation process has the following drawbacks: (1) high cost due to reliance on energy-intensive equipment and expensive reagents; (2) complex operation requiring precise control of multiple parameters and low tolerance for error; (3) high safety risks involving high temperature and pressure, corrosive substances, and potential leaks of toxic substances; and (4) heavy environmental burden, with fossil raw materials and artificially synthesized organic materials still being the mainstream raw materials, resulting in both high carbon emissions and chemical pollution. These drawbacks severely restrict the industrial production and application of carbon foam, necessitating the development of a more economical, simple, safe, and environmentally friendly new carbon foam preparation process. Summary of the Invention

[0011] In view of this, the purpose of this invention is to provide a waste paper-based carbon foam that can be used for interfacial photoevaporation seawater desalination, as well as its preparation method and application. The preparation method provided by this invention is economical, simple, safe and environmentally friendly. The carbon foam material obtained can efficiently convert solar energy into thermal energy and localize it at the gas-liquid interface, thereby achieving efficient and continuous evaporation of water molecules at the evaporation interface.

[0012] This invention provides a method for preparing waste paper-based carbon foam that can be used for interfacial photoevaporation seawater desalination, comprising the following steps:

[0013] a) Cut paper waste into pieces, then grind them to obtain paper powder;

[0014] b) Manganese acetate tetrahydrate, ferric nitrate nonahydrate, and citric acid monohydrate are mixed and ground to obtain a manganese-iron-citric acid slurry;

[0015] There is no order requirement for steps a) and b).

[0016] c) The paper powder and manganese-iron-citric acid slurry are mixed, then kneaded and shaped to obtain carbon foam precursor;

[0017] d) The carbon foam precursor is calcined under limited oxygen conditions to obtain waste paper-based carbon foam.

[0018] Preferably, in step a), the paper waste includes one or more of the following: waste corrugated cardboard, waste printing paper, waste newspaper, waste kraft paper, waste magazine paper, waste coated printing paper, and waste toilet paper.

[0019] Preferably, in step a), the planar dimensions of the fragment are (0.5cm × 0.5cm) to (1.5cm × 1.5cm).

[0020] Preferably, in step a), the particle size of the paper powder is 50-200 mesh.

[0021] Preferably, in step b), the molar ratio of manganese acetate tetrahydrate to ferric nitrate nonahydrate is 1:(1~3.5); the molar ratio of the total amount of manganese acetate tetrahydrate and ferric nitrate nonahydrate to citric acid monohydrate is 1:(2~3).

[0022] Preferably, in step b), the determination of whether the mixing and grinding is complete is that there are no more particulate matter in the slurry.

[0023] Preferably, in step c), the mass ratio of the paper powder to the manganese-iron-citric acid slurry is 1:(5~7.5).

[0024] Preferably, in step d), the heating rate of the calcination is 1~10℃ / min, the final temperature is 350~650℃, and the holding time is 0.5~6h.

[0025] This invention provides a waste paper-based carbon foam that can be used for interfacial photoevaporation seawater desalination, prepared according to the preparation method described in the above technical solution.

[0026] This invention provides an application of the waste paper-based carbon foam described in the above-mentioned technical solution in interfacial photoevaporation seawater desalination.

[0027] Compared with existing technologies, this invention provides a waste paper-based carbon foam that can be used for interfacial photoevaporation seawater desalination, its preparation method, and its application. The preparation method provided by this invention includes the following steps: a) cutting waste paper into fragments and then grinding them to obtain paper powder; b) mixing and grinding manganese acetate tetrahydrate, ferric nitrate nonahydrate, and citric acid monohydrate to obtain a manganese-iron-citric acid slurry; steps a) and b) are not sequentially restricted; c) mixing the paper powder and the manganese-iron-citric acid slurry, then kneading and shaping to obtain a carbon foam precursor; d) calcining the carbon foam precursor under oxygen-limited conditions to obtain waste paper-based carbon foam. The preparation method provided by this invention is economical, simple, safe, and environmentally friendly. The resulting carbon foam material can efficiently convert solar energy into thermal energy and localize it at the gas-liquid interface, achieving efficient and continuous evaporation of water molecules at the evaporation interface. More specifically, this invention has at least the following beneficial effects:

[0028] (1) This invention uses paper waste as a cheap carbon source to realize the resource utilization of solid waste and reduce raw material costs. It innovatively utilizes the self-sponging pulping characteristics of dry grinding of metal salts and citric acid, and achieves self-crosslinking molding by means of the swelling effect of cellulose and its coordination with iron and manganese ions. No solvents need to be added throughout the process, completely avoiding the generation of waste liquid; and no adhesives are needed, avoiding adhesive residues and their impact on the material properties and structure.

[0029] (2) The present invention can complete the preparation of carbon foam by mechanical crushing, dry pulping, kneading and molding and one-step calcination, which greatly shortens the production cycle and reduces costs. There is no high-pressure liquid phase reaction step in the whole process, which completely eliminates the dependence of traditional processes on closed high-pressure equipment.

[0030] (3) The present invention produces shaped carbon foam through a simple process. Its abundant macroporous and mesoporous structure provides water transport channels, metal oxide particles enhance the hydrophilicity of the pore walls, and the carbonized structure endows the material with photothermal conversion properties. Therefore, this waste paper-based carbon foam can be used as an interfacial photoevaporation seawater desalination material with great potential for promotion. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0032] Figure 1 This is a photographic demonstration of the carbon foam preparation process in Example 1 of the present invention;

[0033] Figure 2 The images show the morphology of the carbon foam prepared in Example 1 of this invention; wherein, (a) is a photograph of the appearance of the carbon foam, (b) is a photograph of the cross section of the carbon foam, (c) is an SEM image of the carbon foam at 5000x magnification, and (d) is an SEM image of the carbon foam at 50000x magnification.

[0034] Figure 3 The pore size distribution curve and pore parameter diagram of the carbon foam prepared in Example 1 of this invention are obtained by mercury intrusion porosimetry.

[0035] Figure 4 The N2 adsorption-desorption curve of the carbon foam prepared in Example 1 of this invention;

[0036] Figure 5 X-ray diffraction pattern of the carbon foam prepared in Example 1 of this invention;

[0037] Figure 6 The image shows the dynamic contact angle measurement results of the carbon foam prepared in Example 1 of this invention.

[0038] Figure 7 The experimental apparatus and experimental results of the carbon foam prepared in Example 1 of this invention are shown in the figure; wherein, (a) is a figure of the experimental apparatus for photothermal heating, (b) is an infrared thermal imaging result of the photothermal heating experiment, and (c) is a figure of photothermal heating curve.

[0039] Figure 8 Physical images of the carbonides prepared in Comparative Examples 1 to 3 provided for the present invention; wherein, (a) is a physical image of Comparative Example 1, (b) is a physical image of Comparative Example 2, and (c) is a physical image of Comparative Example 3.

[0040] Figure 9 Photographs and results of the photothermal evaporation experiment provided for application example 1 of the present invention; wherein, (a) is a photograph of the experiment with carbon foam, (b) is a photograph of the blank control experiment, and (c) is a graph showing the change in the mass of seawater evaporation under different conditions.

[0041] Figure 10 Photographs and experimental results of an outdoor seawater desalination experiment provided for application example 2 of the present invention; wherein, (a) is a schematic diagram of the outdoor seawater desalination experimental device, and (b) is a comparison diagram of the concentrations of Na, K, Mg and Ca ions in seawater and condensate.

[0042] Appendix Figure 10 Labeling explanation: 1 is water vapor, 2 is carbon foam, 3 is seawater, and 4 is condensate. Detailed Implementation

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] This invention provides a method for preparing waste paper-based carbon foam that can be used for interfacial photoevaporation seawater desalination, comprising the following steps:

[0045] a) Cut paper waste into pieces, then grind them to obtain paper powder;

[0046] b) Manganese acetate tetrahydrate, ferric nitrate nonahydrate, and citric acid monohydrate are mixed and ground to obtain a manganese-iron-citric acid slurry;

[0047] There is no order requirement for steps a) and b).

[0048] c) The paper powder and manganese-iron-citric acid slurry are mixed, then kneaded and shaped to obtain carbon foam precursor;

[0049] d) The carbon foam precursor is calcined under limited oxygen conditions to obtain waste paper-based carbon foam.

[0050] In the preparation method provided by the present invention, in step a), the main components of the paper waste include cellulose, hemicellulose and lignin, which can be converted into carbon materials through pyrolysis and carbonization.

[0051] In the preparation method provided by the present invention, in step a), the paper waste includes, but is not limited to, one or more of waste corrugated cardboard, waste printing paper, waste newspaper, waste kraft paper, waste magazine paper, waste coated printing paper and waste toilet paper, preferably waste corrugated cardboard.

[0052] In the preparation method provided by the present invention, in step a), the waste paper is first cut to a size suitable for the grinding machine, and then the fragments are ground into paper powder in the grinding machine to meet the requirements of the physical state of the raw materials in the subsequent mixing and molding steps. The grinding time should be set reasonably. If the time is too short, the waste paper cannot be powdered. If the time is too long, the waste paper powder will be too fine, the degree of cross-linking between fibers will be low during the kneading and calcination process, and the mechanical strength of the final material will be reduced.

[0053] In the preparation method provided by the present invention, in step a), the planar size of the fragment is preferably (0.5cm×0.5cm)~(1.5cm×1.5cm), more preferably 1cm×1cm.

[0054] In the preparation method provided by this invention, in step a), the grinding step involves filling the processing chamber of a grinder with paper scraps and pulverizing the paper scraps into a uniform powder, so that no more visible paper scraps remain. The grinding time is preferably 2 to 4 minutes, specifically 2 minutes, 2.5 minutes, 3 minutes, 3.5 minutes, or 4 minutes.

[0055] In the preparation method provided by the present invention, in step a), the particle size of the paper powder is preferably 50-200 mesh, more preferably 80-120 mesh.

[0056] In the preparation method provided by this invention, in step b), manganese acetate tetrahydrate, ferric nitrate nonahydrate, and citric acid monohydrate are thoroughly mixed and ground in a mortar at a certain molar ratio. The mechanical energy provided by the grinding process directly destroys the crystal structure, forcibly releasing the water of crystallization from manganese acetate tetrahydrate, ferric nitrate nonahydrate, and citric acid. These released water molecules are not simply free, but are absorbed by the highly hygroscopic Fe... 3+ and Mn 2+ Rapid capture occurs. Due to the high charge density of transition metal ions, their strong affinity for water molecules causes dense hydration of water molecules on the surface of salt particles, forming a locally high-concentration ion solution layer. Simultaneously, the intense mixing action of grinding forces the viscous, micro-soluble layer formed after hygroscopic absorption to be repeatedly exposed, compressed, and fused, causing water molecules to redistribute between particles. Ultimately, the released lattice water, acting as an in-situ liquid medium, forms a continuous, viscous hydration network dominated by the hygroscopicity of the metal salt, encapsulating and uniformly dispersing the incompletely dissolved solid particles, thus achieving the transformation from particulate matter to a slurry.

[0057] In the preparation method provided by the present invention, in step b), the criterion for determining that the mixing and grinding is complete is that there are no more particulate matter in the slurry.

[0058] In the preparation method provided by this invention, in step c), paper powder and manganese-iron-citric acid slurry need to be mixed evenly in a certain proportion, and then fully kneaded and shaped under mechanical action. The main component of paper powder is cellulose, which can rapidly adsorb free water and ion solution in the slurry through hydroxyl groups, causing the fibers to swell and form a flexible gel network; at the same time, metal ions (Mn) 2+ / Fe 3+ The cellulose ions coordinate with the hydroxyl and carboxyl groups of cellulose to form "ion-ligand" bridges, enhancing the network rigidity. Under the mechanical action of thorough kneading, shear force causes the swollen fibers to intertwine and extend, squeezing the slurry liquid phase into the fiber gaps to achieve densification. Based on the formation of metal ion crosslinks and the physical entanglement of the cellulose hydrogen bond network, a thixotropic three-dimensional network structure is finally formed—"ion-ligand" crosslinks provide viscosity, while the cellulose skeleton maintains strength, thus forming a plastic dough-like material, namely a carbon foam precursor.

[0059] In the preparation method provided by the present invention, in step c), the shape of the molding is preferably a disc.

[0060] In the preparation method provided by this invention, the proportions of each component in steps b) to c) are crucial to the formation of the precursor and carbon foam: when manganese acetate tetrahydrate is in excess, its low lattice water content and weak hygroscopicity lead to insufficient free water in the system; if ferric nitrate nonahydrate is in excess, the high concentration of nitrate ions rapidly decomposes at around 160°C, releasing strong oxidizing gases (such as NO2), causing severe oxidative erosion of the cellulose skeleton before it is fully carbonized, resulting in a sharp reduction in early structural strength. More importantly, the low-viscosity molten salt phase formed by ferric nitrate above 200°C will penetrate into the uncured carbon skeleton, causing the material to exhibit liquid-like rheological behavior, losing its self-supporting ability, and the combined effect of gas expansion and molten flow will prevent the final material from being formed. The gases released by the thermal decomposition of citric acid (such as CO, H2, CH4) are used as foaming agents, and their release rate needs to be related to the metal ions (Fe). 3 + / Mn 2+The catalytic carbonization process is matched to form a viscous mesophase to stabilize bubbles; too little citric acid leads to insufficient gas and foam collapse, while too much causes violent gas production to break through the thermoplastic system, resulting in foam coalescence or structural collapse. When there is too little paper dust, the sparse fiber network cannot effectively lock in the free water released from the metal salt slurry, making the precursor difficult to shape during kneading; at the same time, the lack of fiber cross-linking points weakens the integrity of the iron-manganese-citric acid network, while excessive paper dust competes for limited moisture, forcing the metal salt and citric acid to exist in an agglomerated state, resulting in the precursor drying, hardening, and cracking. Therefore, Fe 3+ With Mn 2+ The proportion of each component regulates the initial pulp rheology and pyrolysis stress, citric acid coordinates the crosslinking strength and foaming behavior, and paper powder cellulose provides the carbonization skeleton. Only by precisely controlling the addition ratio of each component can the gradual evolution from pulp to plastic precursor to complete carbon foam be achieved.

[0061] In the preparation method provided by this invention, in steps b) to c), the molar ratio of manganese acetate tetrahydrate to ferric nitrate nonahydrate is preferably 1:(1~3.5), specifically 1:1, 1:1.2, 1:1.5, 1:1.7, 1:2, 1:2.3, 1:2.5, 1:2.7, 1:3, 1:3.2, or 1:3.5; the molar ratio of the total amount of manganese acetate tetrahydrate and ferric nitrate nonahydrate to citric acid monohydrate is preferably 1:(2~3), specifically... The ratio of paper powder to manganese-iron-citric acid slurry is preferably 1:(5~7.5), specifically 1:5, 1:5.2, 1:5.5, 1:5.7, 1:6, 1:6.2, 1:6.5, 1:6.7, 1:7, 1:7.2 or 1:7.5.

[0062] In the preparation method provided by this invention, in step d), a homogeneous mixture of paper powder and manganese-iron-citric acid slurry (i.e., carbon foam precursor) is calcined to pyrolyze and carbonize it into carbon foam. To ensure complete pyrolysis of the organic components in the paper powder and to avoid the carbon skeleton derived from the paper powder from burning and ashing at high temperatures, the calcination process should be carried out under oxygen-limited conditions, and the calcination temperature and time should be set appropriately.

[0063] In the preparation method provided by the present invention, in step d), the calcination equipment is preferably a muffle furnace; the specific calcination method preferably includes: placing the precursor in a crucible, covering it and wrapping it with at least two layers of aluminum foil, and then placing it in a muffle furnace for calcination.

[0064] In the preparation method provided by this invention, in step d), the heating rate of calcination is preferably 1~10℃ / min, specifically 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min; the final temperature of calcination is preferably 350~650℃, specifically 350℃, 370℃, 400℃, 420℃, 450℃, 470℃, 500℃, 520℃, 550℃, 570℃, 600℃, 620℃ or 650℃; the holding time of calcination is preferably 0.5~6h, specifically 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h.

[0065] For clarity, the following detailed description is provided through examples, comparative examples, and application examples.

[0066] Example 1

[0067] The preparation process of waste paper-based carbon foam that can be used for interfacial photoevaporation seawater desalination is as follows:

[0068] (1) Cut the waste corrugated cardboard into square fragments of 1cm×1cm, take an appropriate amount of waste corrugated cardboard fragments and place them in the sample chamber of the grinder, grind and crush for 2 minutes to obtain waste corrugated cardboard powder (80~120 mesh).

[0069] (2) Take 0.6127g (0.0025mol) manganese acetate tetrahydrate, 2.02g (0.005mol) ferric nitrate nonahydrate and 3.9401g (0.01875mol) citric acid monohydrate and place them in an agate mortar and grind them thoroughly into a uniform slurry.

[0070] (3) Add 1g of waste corrugated paper powder to manganese-iron-citric acid slurry, mix thoroughly and knead until dough-like, and further shape into a cake-like form, i.e. carbon foam precursor.

[0071] (4) Place the carbon foam precursor in a corundum crucible, cover it and wrap it with two layers of aluminum foil, then put it in a muffle furnace and heat it to 600°C at a rate of 2°C / min. Hold it for 2 hours to obtain waste paper-based carbon foam.

[0072] Figure 1 The image shows a photographic demonstration of the carbon foam preparation process in Example 1 of this invention.

[0073] Figure 2 This is a morphological image of the carbon foam prepared in Example 1 of the present invention. Wherein, Figure 2 (a) A photograph of the carbon foam prepared in Example 1, showing a black molded structure with a diameter of approximately 3.5 cm; Figure 2 (b) A cross-sectional photograph of the carbon foam prepared in Example 1, showing that it has a large number of macroscopic pores inside; Figure 2 (c) is a scanning electron microscope (SEM) image of carbon foam at 5000x magnification, showing that it has a large number of micron-sized pores, proving that significant foaming behavior occurred during the preparation process; Figure 2 (d) is a scanning electron microscope (SEM) image of the carbon foam at 50,000x magnification, showing that it has a large number of nanoscale pores. The above results indicate that the carbon foam forms a well-developed porous structure thanks to the pyrolysis and foaming behavior during the thermal conversion process.

[0074] Figure 3 The mercury intrusion porosimetry pore size distribution curve and pore parameter diagram of the carbon foam prepared in Example 1 of this invention are used to reflect the macroporous (pore size > 100 nm) structure of the material. The results show that the pore size distribution curve of the carbon foam has a steep and narrow single main peak at 116.9 μm. This sharp peak indicates that the material has a large number of uniformly sized macroporous structures. In addition, its porosity is as high as 74.97%, which also verifies the high porosity characteristics of the material.

[0075] Figure 4 The N2 adsorption-desorption curves of the carbon foam prepared in Example 1 of this invention are used to reflect the microporous (pore size < 2 nm) and mesoporous (2 nm < pore size < 50 nm) structure of the material. The results show that the adsorption capacity of the carbon foam increases sharply in the low relative pressure region (P / P0 < 0.1), revealing the presence of numerous micropores, which dominate 86.33% of the total pore volume. The hysteresis loop in the medium-high relative pressure region (0.4 < P / P0 < 1) indicates the occurrence of capillary condensation, suggesting the existence of a mesoporous structure within the material, but the mesoporous volume accounts for only 16.30% of the total volume. Near the saturation pressure, the simultaneous sharp increase in adsorption / desorption further confirms the macroporous permeability characteristics, echoing the mercury porosimetry data. The material as a whole is centered on micropores with an average pore size of 1.78 nm, while also possessing a pore size of 93.81 nm. 2 / g high specific surface area and 0.0417cm 3 The total pore volume is / g, and it has a unique hierarchical pore structure of "macropore framework-micropore wall".

[0076] Figure 5 The X-ray diffraction (XRD) pattern of the carbon foam prepared in Example 1 of this invention is shown. The results show that the carbon foam has a series of sharp diffraction peaks, proving that the carbon matrix contains manganese ferrite (MnFe2O4), which is produced by the pyrolysis conversion of iron-manganese-citric acid slurry in the raw materials.

[0077] Figure 6The image shows the dynamic contact angle measurement results of the carbon foam prepared in Example 1 of this invention. The results show that the droplet can be completely absorbed within 60 ms after contacting the carbon foam surface, indicating that the material has good hydrophilicity.

[0078] Figure 7 The experimental apparatus and results for the photothermal heating of the carbon foam prepared in Example 1 of this invention are shown. Figure 7 As shown in (a), the carbon foam prepared in Example 1 was irradiated with the illumination of a standard sun using a xenon lamp. Figure 7 (b) is an infrared thermal image of carbon foam after irradiation for 1110 s, with a surface temperature as high as 73°C. Figure 7 (c) shows that after 30 seconds of illumination, the surface temperature of the carbon foam rapidly increased from 23°C to 48°C, indicating the occurrence of photothermal conversion. After 210 seconds of illumination, the rate of change of the material surface temperature slowed down, eventually reaching 73°C at 1110 seconds.

[0079] Example 2

[0080] The preparation process of waste paper-based carbon foam that can be used for interfacial photoevaporation seawater desalination is as follows:

[0081] (1) Cut waste newspaper into 1cm×1cm square pieces, take an appropriate amount of waste newspaper pieces and place them in the sample chamber of the grinder, grind and crush for 2 minutes to obtain waste newspaper powder (80~120 mesh).

[0082] (2) Take 3.0635g (0.0125mol) manganese acetate tetrahydrate, 5.05g (0.0125mol) ferric nitrate nonahydrate and 13.134g (0.0625mol) citric acid monohydrate and place them in an agate mortar and grind them thoroughly into a uniform slurry.

[0083] (3) Add 3.75g of waste corrugated paper powder to iron-manganese-citric acid slurry, mix thoroughly and knead until dough-like, and further shape into a cake shape, i.e. carbon foam precursor.

[0084] (4) Place the carbon foam precursor in a corundum crucible, cover it and wrap it with two layers of aluminum foil, then put it in a muffle furnace and heat it to 550°C at a rate of 4°C / min. Hold it for 5 hours to obtain waste paper-based carbon foam.

[0085] The waste paper-based carbon foam prepared in this embodiment was tested, and the results showed that the porosity of the sample was 80.19%. After irradiating the sample with the light of a standard sun for 1200 seconds using a xenon lamp, its surface temperature could rise to 78°C.

[0086] Example 3

[0087] The preparation process of waste paper-based carbon foam that can be used for interfacial photoevaporation seawater desalination is as follows:

[0088] (1) Cut the waste printing paper into square fragments of 1cm×1cm, take an appropriate amount of waste printing paper fragments and place them in the sample chamber of the grinder, grind and crush for 3 minutes to obtain waste printing paper powder (80~120 mesh).

[0089] (2) Take 0.6127g (0.0025mol) manganese acetate tetrahydrate, 3.03g (0.0075mol) ferric nitrate nonahydrate and 4.2028g (0.02mol) citric acid monohydrate and place them in an agate mortar and grind them thoroughly into a uniform slurry.

[0090] (3) Add 1.5g of waste corrugated paper powder to iron-manganese-citric acid slurry, mix thoroughly and knead until dough-like, and further shape into a cake shape, i.e. carbon foam precursor.

[0091] (4) Place the carbon foam precursor in a corundum crucible, cover it and wrap it with two layers of aluminum foil, then put it in a muffle furnace and heat it to 650°C at a rate of 5°C / min. Hold it for 3 hours to obtain waste paper-based carbon foam.

[0092] The waste paper-based carbon foam prepared in this embodiment was tested, and the results showed that the porosity of the sample was 78.23%. After irradiating the sample with the light of a standard sun for 1000 seconds using a xenon lamp, its surface temperature could rise to 67°C.

[0093] Comparative Example 1

[0094] (1) Cut the waste corrugated cardboard into square fragments of 1cm×1cm, take an appropriate amount of waste corrugated cardboard fragments and place them in the sample chamber of the grinder, grind and crush for 2 minutes to obtain waste corrugated cardboard powder (80~120 mesh).

[0095] (2) Take 3.03g (0.0075mol) ferric nitrate nonahydrate and 3.9401g (0.01875mol) citric acid monohydrate and place them in an agate mortar and grind them thoroughly into a uniform slurry.

[0096] (3) Add 1g of waste corrugated paper powder to iron-citric acid slurry, mix thoroughly and knead until dough-like, and further shape into a cake shape, i.e., precursor.

[0097] (4) Place the precursor in a corundum crucible, cover it and wrap it with two layers of aluminum foil, then put it in a muffle furnace and heat it to 600°C at a rate of 2°C / min. Hold it for 2 hours to obtain carbon.

[0098] like Figure 8 As shown in (a), the resulting carbonized material cannot be formed and appears as irregular cracked flakes, making it unsuitable for interfacial evaporation seawater desalination.

[0099] Comparative Example 2

[0100] (1) Cut the waste corrugated cardboard into square fragments of 1cm×1cm, take an appropriate amount of waste corrugated cardboard fragments and place them in the sample chamber of the grinder, grind and crush for 2 minutes to obtain waste corrugated cardboard powder (80~120 mesh).

[0101] (2) Take 3.03g (0.0075mol) ferric nitrate nonahydrate and 3.9401g (0.01875mol) citric acid monohydrate and place them in an agate mortar and grind them thoroughly into a uniform slurry.

[0102] (3) Add 1.12g of waste corrugated paper powder to iron-citric acid slurry, mix thoroughly and knead until dough-like, and further shape into a cake shape, i.e., precursor.

[0103] (4) Place the precursor in a corundum crucible, cover it and wrap it with two layers of aluminum foil, then put it in a muffle furnace and heat it to 600°C at a rate of 2°C / min. Hold it for 2 hours to obtain carbon.

[0104] like Figure 8 As shown in (b), although a molded material can be obtained in the end, it is in the form of a sheet and does not have a foam structure, so it cannot be used for interfacial evaporation seawater desalination.

[0105] Comparative Example 3

[0106] (1) Cut the waste corrugated cardboard into square fragments of 1cm×1cm, take an appropriate amount of waste corrugated cardboard fragments and place them in the sample chamber of the grinder, grind and crush for 2 minutes to obtain waste corrugated cardboard powder (80~120 mesh).

[0107] (2) Take 3.03g (0.0075mol) ferric nitrate nonahydrate and 3.9401g (0.01875mol) citric acid monohydrate and place them in an agate mortar and grind them thoroughly into a uniform slurry.

[0108] (3) Add 1.45g of waste corrugated paper powder to iron-citric acid slurry, mix thoroughly and knead until dough-like, and further shape into a cake shape, i.e., precursor.

[0109] (4) Place the precursor in a corundum crucible, cover it and wrap it with two layers of aluminum foil, then put it in a muffle furnace and heat it to 600°C at a rate of 2°C / min. Hold it for 2 hours to obtain carbon.

[0110] like Figure 8 As shown in (c), no significant foaming phenomenon occurred during the preparation process, and the obtained product was in the form of a cake with a dense structure, which could not be used for interfacial evaporation seawater desalination.

[0111] Application Example 1

[0112] like Figure 9As shown in (a), 140 mL of natural seawater filtered through a 0.22 μm filter membrane was placed in a glass beaker; the carbon foam prepared in Example 1 was embedded in the center of a pearl cotton foam ring and placed on the water surface, with the bottom of the carbon foam in direct contact with the seawater and its upper surface above the water surface; a xenon lamp was used to provide it with the illumination of one standard sun to achieve interfacial photothermal evaporation. In the blank control experiment, only the pearl cotton foam ring was placed on the water surface, and other experimental conditions were kept consistent. Figure 9 (b)). The experimental results are as follows: Figure 9 As shown in (c), with the assistance of carbon foam, thanks to the interfacial photothermal conversion process, the evaporation rate of seawater reached 0.80 g within 1 hour; in the blank control experiment, the evaporation rate of seawater under the same conditions was only 0.34 g. The above experimental results show that, based on the photothermal conversion performance of carbon foam itself, the evaporation efficiency of seawater can be significantly improved.

[0113] Application Example 2

[0114] An outdoor seawater desalination experiment was conducted using the carbon foam prepared in Example 2. A schematic diagram of the experimental setup is shown below. Figure 10 As shown in (a), under sunlight, a carbon foam evaporator generates water vapor. This water vapor condenses upon contact with a cooler glass top surface, forming water droplets. These droplets accumulate and drip, eventually being collected as fresh water. Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to determine the Na+ content in real seawater and condensate. + K + Mg 2+ Ca 2+ The concentration, the results are as follows Figure 10 As shown in (b), its concentration was 1.29 × 10⁻⁶. 4 mg / L, 5.53×10 2 mg / L, 1.49×10 3 mg / L, 5.60×10 2 The concentrations of carbon foam decreased to 0.55 mg / L, 0.11 mg / L, 0.21 mg / L, and 0.12 mg / L, demonstrating the feasibility of applying carbon foam to interfacial photoevaporation seawater desalination.

[0115] The above description provides an illustrative overview of the present invention and its embodiments. This description is not restrictive, and the embodiments shown are merely one example of the invention's implementation. Actual implementations are not limited to these examples. Therefore, if those skilled in the art are inspired by this description and design similar implementations and examples without departing from the spirit of the invention, such designs should fall within the scope of protection of the present invention.

Claims

1. A method for preparing waste paper-based carbon foam that can be used for interfacial photoevaporation seawater desalination, characterized in that, Includes the following steps: a) Cut paper waste into pieces, then grind them to obtain paper powder; b) Manganese acetate tetrahydrate, ferric nitrate nonahydrate, and citric acid monohydrate are mixed and ground to obtain a manganese-iron-citric acid slurry; There is no order requirement for steps a) and b). c) The paper powder and manganese-iron-citric acid slurry are mixed, then kneaded and shaped to obtain carbon foam precursor; d) The carbon foam precursor is calcined under limited oxygen conditions to obtain waste paper-based carbon foam.

2. The preparation method according to claim 1, characterized in that, In step a), the paper waste includes one or more of the following: waste corrugated cardboard, waste printing paper, waste newspaper, waste kraft paper, waste magazine paper, waste coated printing paper, and waste toilet paper.

3. The preparation method according to claim 1, characterized in that, In step a), the planar dimensions of the fragment are (0.5cm × 0.5cm) to (1.5cm × 1.5cm).

4. The preparation method according to claim 1, characterized in that, In step a), the particle size of the paper powder is 50~200 mesh.

5. The preparation method according to claim 1, characterized in that, In step b), the molar ratio of manganese acetate tetrahydrate to ferric nitrate nonahydrate is 1:(1~3.5); the molar ratio of the total amount of manganese acetate tetrahydrate and ferric nitrate nonahydrate to citric acid monohydrate is 1:(2~3).

6. The preparation method according to claim 1, characterized in that, In step b), the criterion for determining that the mixing and grinding is complete is that there are no more particulate matter in the slurry.

7. The preparation method according to claim 1, characterized in that, In step c), the mass ratio of the paper powder to the manganese-iron-citric acid slurry is 1:(5~7.5).

8. The preparation method according to claim 1, characterized in that, In step d), the heating rate of the calcination is 1~10℃ / min, the final temperature is 350~650℃, and the holding time is 0.5~6h.

9. A waste paper-based carbon foam that can be used for interfacial photoevaporation seawater desalination, characterized in that, Prepared according to the preparation method according to any one of claims 1 to 8.

10. The application of the waste paper-based carbon foam according to claim 9 in interfacial photoevaporation seawater desalination.

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