Sulfonated activated carbon for water capturing

Abstract

The present invention relates to a surface-modified activated carbon material comprising activated carbon material and a plurality of sulfonate, sulfite, sulfate or sulfone groups, wherein the surface-modified activated carbon material comprises sulfur in an amount of at least 3.0 wt % and to the use of the surface-modified activated carbon material for capturing or harvesting water.

Description

SULFONATED ACTIVATED CARBON FOR WATER CAPTURINGField of the Invention

[0001] The present invention relates to the field of water capturing and in particular to the use of sulfonated activated carbon for capturing water from a water containing environment.Background Art

[0002] According to the United Nations, about one third of the global population lacks access to safely managed drinking water and sanitation services. In response, the United Nations' Sustainable Development Goal (UN SDG) #6 aims to ensure access to sanitation and clean water for everyone by the year 2030. At present, the availability of drinking water is largely tied to geographical location and dependent on naturally occurring sources such as rivers, lakes and precipitation. To meet the targets of UN SDG #6, substantial improvements in prevailing water collection and purification methods are imperative. Desalination of seawater holds promise as an alternative approach for freshwater production, however, it is generally energy-intensive and requires access to large bodies of salty water, rendering it unsuitable for landlocked regions.

[0003] Atmospheric water harvesting (AWH) has emerged as a potential solution for the production of supplementary fresh water due to applicability in almost all regions of the world. The amount of airborne water is estimated to be 1.3 x 1016L globally, exceeding the volume in all of the world’s rivers combined by a factor of approximately six (2.1 x 1015L). At present, there are four prevailing approaches for collecting water from air, which include fog collectors, refrigeration methods, as well as membrane- and adsorption-based systems. In the process of fog harvesting, water vapor can be condensed as dew on cold, flat surfaces without the requirement of further external energy input. Despite its efficiency, fog collectors are limited by the need for high relative humidity (RH), making them impractical for numerous arid geographical regions, which are typically those most susceptible to water stress. In refrigeration-based systems atmospheric water vapor is cooled below the dew point to initiate condensation, limiting their applicability in areas with low RH due to increased energy requirements. In contrast, membrane-based systems can operate efficiently in low RH environments. However, they suffer from low selectivity and high energy demands as a vacuum is required to create a pressure gradient across membranes, the product of which is then cooled to triggercondensation and, hence, water harvesting. In adsorption-based atmospheric water harvesting (AWH) methods, hygroscopic sorbent materials are used to passively capture water from the atmosphere and concentrate it on their surfaces from where it can be desorbed in a controlled manner upon the application of a specific trigger, such as heat.

[0004] An ideal sorbent for AWH should exhibit high stability upon repeated exposure to water and heat, good working capacities at low RH, and a moderate heat of adsorption to minimize the energy required for water desorption. Despite exhibiting good water-sorption capacities, classical drying agents such as zeolites and hygroscopic metal salts commonly face challenges associated with elevated adsorption enthalpies, rendering the release of water an energetically demanding process. Metal-organic frameworks (MOFs), a category of porous materials comprising metal ions or clusters connected by organic ligands, demonstrate potential for AWH due to their impressive uptake capacities and low enthalpies of adsorption. Although some MOFs have been successfully implemented in large- scale devices, the practical applicability of vast swathes of MOFs is impeded by their sensitivity to water, resulting in network degradation. Additionally, the synthesis of MOFs is often cumbersome and expensive, currently rendering them an uneconomical option for widespread use. To address these problems, recent research on AWH has directed its attention to fully organic sorbents, such as hygroscopic porous polymers (HPPs). Besides offering diverse synthetic routes and a plethora of chemical functionalities, these materials are characterized by high surface areas, tunable textural properties, and excellent chemical, thermal, and mechanical stabilities. Hydrogels, a subclass of HPPs, comprising of highly hydrophilic polymeric networks and a significant amount of water, display excellent absolute water uptake capacity and sufficient heat of adsorption. However, their poor water uptake at RH of below 30% renders many candidates unsuitable for application in arid regions. Another common group of HPPs are covalent organic frameworks (COFs), which are reticular materials synthesized from molecular organic building blocks, enabling the bottom-up design of specific chemistries and textural properties beneficial for AWH. While COFs have proven to be excellent candidates for AWH, challenges related to scale-up and production cost currently still impede their commercial viability. Recently, the synthesis and implementation of a low-cost, organic sulfonated hyper crosslinked polymer for AWH was reported,reaching a total water uptake capacity of 0.81 g-g1from humid air (90% RH) in comparison to only 0.07 g-g1using a non-functionalized equivalent (Schweng, P. et al., Small 2023, 19, 2304562(1-8)).

[0005] WO2022178645A1 describes a nanoporous carbonaceous material for water adsorption. The nanoporous carbonaceous material comprises at least one pyrolyzed organic compound-formaldehyde resin and may optionally be functionalized. Zhu et al. (2019) report sulfur-doped activated carbons prepared from polythiophene for acetone removal. Xiao et al. (2013) describe surface- modified activated carbon for water adsorption at various relative humidity levels.

[0006] However, there is still the need for improved materials for atmospheric water harvesting.Summary of invention

[0007] It is the object of the present invention to provide improved materials for water harvesting / adsorption from a water containing environment. The object is solved by the subject matter of the present invention.

[0008] The present invention relates to surface-modified activated carbon material comprising activated carbon and sulfur, wherein the sulfur is comprised as sulfonate, sulfite, or sulfone groups and is present in an amount of at least 3.0 wt.%.

[0009] The activated carbon and the sulfur containing groups are covalently bound.

[0010] The amount of sulfur in the surface-modified activated carbon material is about 3.0 to 30.0 wt.%, or about 3.5 to 30.0 wt.%, or about 4.0 to 30.0 wt.%, or about or about 4.5 to 30.0 wt.%, or 3.0 to 25.0 wt.%, or about 3.5 to 25.0 wt.%, or about 4.0 to 25.0 wt.%, or about or about 4.5 to 25.0 wt.%, or 3.0 to 20.0 wt.%, or about 3.5 to 20.0 wt.%, or about 4.0 to 20.0 wt.%, or about or about 4.5 to 20.0 wt.%, or about 3.0 to 15.0 wt.%, or about 3.5 to 15.0 wt.%, or about 4.0 to 15.0 wt.%, or about 4.5 to 15.0 wt.%, or about 5.0 to 15.0 wt.%, or about 3.0 to 10.0 wt.%, or about 3.5 to 10.0 wt.%, or about 4.0 to 10.0 wt.%, or about 4.5 to 10.0 wt.%, or about 5.0 to 10.0 wt.%, or about 3.0 to 8.0 wt.%, or about 3.5 to 8.0 wt.%, or about 4.0 to 8.0 wt.%, or about 4.5 to 8.0 wt.%, or about 5.0 to 8.0 wt.%, or about 5.0 to 6.5 wt.%.

[0011] In one embodiment, the amount of sulfur in the surface-modified activated carbon material is about 3.0 to 30.0 wt.%, or 3.5 to 20.0 wt.%, or about 4.0 to 15.0 wt.%, or about 4.5 to 10%, or about 5.0 to 6.5 wt.%

[0012] The elemental composition of the surface-modified activated carbon material may be derived by X-ray photoelectron spectroscopy (XPS) analysis or elemental analysis (EA).

[0013] One embodiment of the invention relates to the use of the surface-modified activated carbon material as described herein in a method of harvesting / adsorbing water from a water containing environment.

[0014] The water containing environment may be, for example, the atmosphere, or gaseous mixtures of various compositions.

[0015] One embodiment of the invention relates to a method for harvesting / adsorbing water from a water containing environment comprising the steps of providing surface-modified activated carbon material; carrying out a water sorption phase for a sufficient period of time; carrying out a water desorption step; and collecting the desorbed water.

[0016] A further embodiment relates to the method as described herein, wherein water desorption step is carried out at a temperature of between 30 to 2000C, or of between 30 to 1500C, or of between 30 to 1000C, or of between 30 to 900C, or of between 40 to 2000C, or of between 40 to 1500C , or of between 40 to 1000C, or of between 40 to 900C, or of between 50 to 2000C, or of between 50 to 1500C, or of between 50 to 1000C, or of between 50 to 900C, or of between 60 to 2000C, or of between 60 to 1500C, or of between 60 to 1000C, or of between 60 to 900C.

[0017] A further embodiment relates to the method as described herein, wherein water desorption step is carried out for at least 1 min, or at least 2 min or at least 5 min, or at least 10 min, or at least 15 min, or at least 30 min, or at least 60 min.

[0018] One embodiment of the invention relates to a method for producing a surface-modified activated carbon material as described herein, comprising the steps of adding a sulfur containing compound; chemically bonding of the sulfur containing group to the surface of the activated carbon, wherein the sulfonated activated carbon comprises at least 3.0 wt % sulfur. The thereby obtained sulfonated activated carbon optionally may be filtered off, dried, washed and / or further purified.

[0019] A further embodiment relates to the method as described herein, wherein the sulfur containing compound is sulfuric acid, chlorosulfonic acid, para-toluene sulfonic acid, sulfuric anhydride, SO3, oleum, sulfamate, thionyl chloride, methanesulfonic acid, trifluoromethanesulfonic acid, trimethylsilyl sulfonic acid, metal bisulfites, or a sulfide, or the like.Brief description of drawings

[0020] Fig. 1: Reaction schemes for sulfonated activated carbon syntheses using a) sulfuric acid or b) chlorosulfonic acid.Fig. 2: FTIR spectra of all activated carbon (AC) and sulfonated activated carbon (SAC or SCAC) sorbents.Fig. 3: X-ray photoelectron C Is spectra of all activated carbon (AC) and sulfonated activated carbon (SAC or SCAC) sorbents.Fig. 4: X-ray photoelectron S 2p spectra of all activated carbon (AC) and sulfonated activated carbon (SAC or SCAC) sorbents.Fig. 5: Thermogravimetric curves for activated carbon (AC) and sulfonated activated carbon (SAC or SCAC) sorbents, measured under air flow (100 mL-min’1), ramped to 7000C at a rate of 100C-min’1.Fig. 6: N2sorption isotherms for all activated carbon (AC) and sulfonated activated carbon (SAC or SCAC) sorbents. Isotherms were measured at -1960C.Fig. 7: Water sorption isotherms for all activated carbon (AC) and sulfonated activated carbon (SAC or SCAC) sorbents. Isotherms were measured at 250C. Fig. 8: Water sorption isotherms of SAC-1 and SCAC-1, recorded at 25 (circles, dashed line), 35 (diamonds, dotted line), and 450C (triangles, solid line).Fig. 9: Dynamic vapor sorption-desorption of a) SAC-1 and b) SCAC-1 at 10%, 20%, 30% and 90% RH.Fig. 10: Desorption of water over time measured with TGA at various temperatures including 300C (wide-dotted line), 450C (narrow-dotted line), 60 C (narrow- dashed line), 750C (wide-dashed line) and 900C (solid line).Fig. 11: Long-term stability of SCAC-1 over 130 adsorption-desorption cycles driven by a humidity-swing between 0 and 40% RH.Fig. 12: Water sorption isotherms of as synthesised SCAC-1 (solid line) and recovered SCAC-1 after sorption-desorption cycles using either simulated sunlight (triangles, dotted line) or heat (diamonds, dashed line) as a trigger for desorption. Fig. 13: N2gas sorption isotherms of as synthesised SCAC-1 (circles) and recovered SCAC-1 after sorption-desorption cycles using either simulated sunlight (triangles) or heat (diamonds) as desorption trigger.Fig. 14: FTI R spectra of as synthesised SCAC-1 (solid line) and recovered SCAC-1 after sorption-desorption cycles using either a humidity-swing (long dash line), simulated sunlight (dashed line), or heat (dotted line) as a trigger for desorption. Fig. 15: TGA curves of as synthesised SCAC-1 (solid line) and recovered SCAC-1 after sorption-desorption cycles using either a humidity-swing (wide-dashed line), simulated sunlight (narrow-dashed line), or heat (dotted line) as a trigger for desorption.Description of Embodiments

[0021] The present invention provides surface-modified activated carbon material comprising activated carbon and a plurality of sulfur groups, wherein the surface- modified activated carbon material comprises sulfur in an amount of at least 3.0 wt %.

[0022] Activated carbon, also called activated charcoal or porous carbon, is a form of carbon commonly used to filter contaminants from water and air, among many other uses. It is processed (activated) to have small, low-volume pores that increase the surface area available for adsorption. Due to its high degree of microporosity, one gram of activated carbon has a surface area in excess of 1 m2, 10 m2, 20 m2, 50 m2, 200 m2, 500 m2, 1,000 m2, 1,500 m2, 2,000 m2, 3,000 m2, 4,000 m2, or 5,000 m2as determined by gas adsorption. Charcoal, before activation, has a specific surface area in the range of 2.0-5.0 m2 / g. High surface areas alone may be sufficient for useful application. Further chemical treatment often enhances adsorption properties.

[0023] Activated carbon is usually derived from waste products such as coconut husks; waste from paper mills has been studied as a source. These bulk sources are converted into charcoal before being 'activated1. When derived from coal it is referred to as activated coal. Activated coke is derived from coke.

[0024] The activated carbon on which sulfur is to be supported is not limited to any particular species but may include activated carbon species obtained by conventional methods using as starting materials, charcoal, coke, coconut shells, natural fibers, synthetic resins such as polyacrylonitrile, rayon and phenol resin, pitch, and the like. The activated carbon may have any form, for example powdery, granular, pellet structure, macaroni structure, fibrous or honeycomb structure.

[0025] “Sulfonate groups” (R — S(=O)2— 0 ), “sulfate groups” (O-SO3H), “sulfone groups” (R — S(=O)2— R’) and “sulfite groups” (SO32) are highly hydrophilic groups.As used herein, the term “sulfite groups” may also encompass sulfite esters (e.g. SMILES (Simplified Molecular Input Line Entry System) of structural formula: S(OR)(OR’)=O).

[0026] The hydrophilicity of other sulfur containing chemical groups, such as sulfhydryl (R — SH) or sulfoxide (R — S(=O) — R1) groups, is not as high when compared to sulfonate, sulfate, sulfite, or sulfone groups. Therefore, sulfonate and / or sulfone activated carbons have a higher uptake of water compared to sulfhydryl or sulfonyl activated carbons.

[0027] One embodiment of the invention relates to a surface-modified activated carbon material wherein the amount of sulfur is at least 3.0 wt.%, preferably 3.0 to 20.0 wt.%, or about 3.5 to 20.0 wt.%, or about 4.0 to 20.0 wt.%, or about or about 4.5 to 20.0 wt.%, or about 3.0 to 15.0 wt.%, or about 3.5 to 15.0 wt.%, or about 4.0 to 15.0 wt.%, or about 4.5 to 15.0 wt.%, or about 5.0 to 15.0 wt.%, or about 3.0 to 10.0 wt.%, or about 3.5 to 10.0 wt.%, or about 4.0 to 10.0 wt.%, or about 4.5 to 10.0 wt.%, or about 5.0 to 10.0 wt.%, or about 3.0 to 8.0 wt.%, or about 3.5 to 8.0 wt.%, or about 4.0 to 8.0 wt.%, or about 4.5 to 8.0 wt.%, or about 5.0 to 8.0 wt.%, or about 5.0 to 6.5 wt.%.

[0028] One embodiment of the invention relates to a surface-modified activated carbon material wherein the amount of sulfur is about 3.0-20 wt.%, preferably about 3.0 wt.%, about 4.0 wt.%, about 5.0 wt.%, about 6.0 wt.%, about 7.0 wt.%, about 8.0 wt.%, about 9.0 wt.%, about 10.0 wt.%, about 11.0 wt.%, about 12.0 wt.%, about 13.0 wt.%, about 14.0 wt.%, about 15.0 wt.%, about 16.0 wt.%, about 17.0 wt.%, about 18.0 wt.%, about 19.0 wt.%, or about 20.0 wt.%.

[0029] One embodiment of the invention relates to the analysis of the elemental composition of the surface surface-modified carbon material as described herein using X-ray photoelectron spectroscopy (XPS) analysis or elemental analysis (EA).

[0030] XPS works under an ultra high vacuum, whereas other methods in the art work under atmospheric conditions and thereby also measure water that may been bound to surface-modified activated carbon material.

[0031] “The water-containing environment” refers to all water-containing environments, which may include but not be limited to gaseous phases, such as air. Water vapor is to be understood as generally being water existing as vapor, i.e., as a barely visible or cloudy diffused form of water, such as water mist, water fumes, or steam, suspended in air. Gaseous water is to be understood as generally beingwater existing in the gas phase. Such water vapor or / and gaseous water exists as either a pure vapor or / and gas of water, or as part of a vapor or / and gas mixture which also includes other vapor or / and gaseous species.

[0032] “Capturing water” as used herein, refers to extraction of water, i.e., to the removal of water from a water containing environment.

[0033] “Harvesting water” as used herein, refers to the extraction and subsequent collection of water.

[0034] One embodiment of the invention relates to capturing or harvesting water from a gaseous phase, e.g., from air. The air may have a relative humidity of equal to or less than 100 %, 90 %, 80 %, 70 %, 60 %, 50 %, 40 %, 30 %, 20%, or less than 10 %.

[0035] A further embodiment relates to the method of capturing or harvesting water from a gaseous phase comprising the steps of providing surface-modified activated carbon material, carrying out a water sorption phase for a sufficient period of time, optionally carrying out a water desorption step, and optionally collecting the desorbed water.

[0036] The water sorption phase is carried out for at least 1 min, 2 min, 3, min, 4 min 5, min, 10 min, 15 min, 30 min, 60 min, 120 min, for at least 3 h, 5 h, 10 h, or for at least 1, 2, or 5 days.

[0037] A further embodiment relates to the method as described herein, wherein the water desorption step is carried out for at least 1 min, 2 min, 3, min, 4 min, 5 min, 10 min, 30 min, 60 min, 120 min, for at least 3 h, 5 h, 10 h, or for at least 1, 2, or 5 days. The water desorption step may be carried out at temperature of between 30 to 2000C, or of between 30 to 1500C, or of between 30 to 1000C, or of between 30 to 900C, or of between 40 to 2000C, or of between 40 to 1500C , or of between 40 to 1000C, or of between 40 to 900C, or of between 50 to 2000C, or of between 50 to 1500C, or of between 50 to 1000C, or of between 50 to 900C, or of between 60 to 2000C, or of between 60 to 1500C, or of between 60 to 1000C, or of between 60 to 900C.

[0038] One embodiment of the invention relates to the method of harvesting water from a gaseous phase, wherein multiple sorption-desorption cycles are employed. A cycle may comprise 1 min, 2 min, 3 min, 4 min, 5 min, 10 min, 30 min, 60 min, 120 min of sorption and 30 min, 60 min, 120 min of desorption. A total of at least 50, 75, 100, 125, 150, 175, or at least 200 cycles may be employed.

[0039] One embodiment of the invention relates to the use of the surface-modified activated carbon material as described herein as a desiccant for adsorption of moisture.

[0040] The surface-modified activated carbon material may also be used as a desiccant for dehumidification, treatment of water damage or leaks, removal of excess water, storage in dry environments, packaging material, preservation, drying of organic solvents, water removal from gas streams, construction materials, kitchen appliances, in heating appliances, ventilation means, in air conditioning (HVAC) systems, as additive in construction materials, or water removal from gas streams, etc.

[0041] The surface-modified activated carbon material used as a desiccant allows to slow down the drying of paint, cement, mortar, and the like. The surface- modified activated carbon material enables a controlled release of the adsorbed water, e.g., by setting and or varying the temperature values.Examples

[0042] The examples which follow are set forth to aid in the understanding of the invention but are not intended to and should not be construed to limit the scope of the invention in any way. The examples do not include detailed descriptions of conventional methods. Such methods are well known to those of ordinary skill in the art.ExperimentalMaterials

[0043] All chemicals were obtained from commercial sources and used without further purification. Activated carbon 1 (AC-1, Technical, Decolorizing Powder, Activated) was purchased from Fisher Chemical™. Activated carbon 2 (AC-2, Norit® GAC 1240W) and activated carbon 3 (AC-3, Norit® RB3), magnesium nitrate hexahydrate (99%), chlorosulfonic acid (99%), and 1,2-dichloroethane (>99%) were purchased from Sigma-Aldrich. Sulfuric acid (95-97%, Fluka™) was purchased from Honeywell Research Chemicals. Methanol (>99.8%) was purchased from Fisher Scientific.Synthesis of sulfonated activated carbon

[0044] CI-SOsH-route: Activated carbon (1.0 g) was first dispersed in 1,2-DCE (15 mL) before the addition of a solution of chlorosulfonic acid (5.0 g, 50 mmol) in 1,2- DCE (5 mL). The reaction was then left to stir overnight. The reaction was slowlydiluted in excess methanol and then filtered from the solution. The resulting product was washed with 50 ml_ of distilled water and subsequently dried at 800C overnight in a vacuum oven. Sulfonated activated carbons obtained using CI-SOsH were labelled SCAC-X.

[0045] l-bSCU-route: Activated carbon (1.0 g) was dispersed in concentrated sulfuric acid (20 mL, 373 mmol) and heated to 1500C for 5 h over stirring. The reaction was left to cool to room temperature before quenching in an ice bath. The resulting product was filtered off and dried at 800C overnight in a vacuum oven. Sulfonated activated carbons obtained using H2SO4- route were labelled SAC-X.Characterization

[0046] All measurements using Fourier-transform infrared spectroscopy (FTIR) were performed at room temperature using a Tensor II FTIR spectrometer (Bruker) equipped with a Bruker Optics Platinum ATR module. IR spectra were measured in the range of 400-4000 cm-1with a spectral resolution of 4 cm-1using the doublesided forward-backward acquisition mode. For each spectrum an average over a total of 32 scans was calculated using a Blackman-Harris 3-term apodization function and a zero-filling factor of 4. During each measurement, the instrument was flushed with dry air and the spectra were recorded and analyzed using the integrated OPUS 7.5 software.

[0047] Nitrogen sorption isotherms were collected at - 1960C on a TriStar II (Micromeritics), controlled using the software TriStar II 3020 version 3.02. Prior to measurement samples were treated overnight at 1200C under N2flow using a FlowPrep 060 (Micromeritics). The acquired data was evaluated using VersaWinTM software version 1.0. Specific surface areas were calculated using the Brunauer- Emmett-Teller (BET) method on the adsorption branch between 0.05-0.2 P / Po. The total pore volume, VTOT, was calculated from the volume of N2 adsorbed at P / Po = 0.97. The micropore volume, VMICRO, was determined using the t-plot method for the relative pressure range between 0.15-0.4.

[0048] X-ray photoelectron spectroscopy (XPS) on a Nexsa Photoelectron Spectrometer (Thermo Scientific) was performed. High-resolution spectra of chlorine (Cl 2p 190-210 eV), and sulphur (S 2p 157-175 eV), carbon (C Is 279-298 eV), nitrogen (N Is 392-410 eV), and oxygen (0 Is 525-545 eV), were recorded with a resolution of 0.1 eV and a pass energy of 50 eV. All measurements were performed using Al-K a X-rays with a spot size of 400 pm. Evaluation of the datawas performed using Avantage software (v5.9931, Thermo Fisher Scientific). The main component in C Is located at 284.8 eV was used to calibrate the spectra and Shirley background was applied for peak fitting. The atomic composition of the sample was determined from the peak area using the integrated scaling factor database ALTHERMO1.

[0049] Thermogravimetric analyses were performed using a Discovery TGA (TA instruments). Around 20 mg of each sample was subjected to heating at a rate of 100C-min - from room temperature to 700 ° C under air gas flow (100 mL-min -)■

[0050] Dynamic vapor sorption (DVS) experiments were performed on a DVS- Resolution (Surface Measurement Systems). For each measurement, approximately 10 mg of sample was weighed into a quartz crystal pan and deionized water was used to generate the desired RH. Unless stated otherwise, each experiment was performed at 250C and each run commenced at 0% RH and was increased to the desired RH for water uptake. Isotherms were recorded up to 90% RH, using a step increment of 10% RH. Each step was equilibrated until the weight change was below 0.02 %-min - prior to data point collection. Long-term stability measurements were carried out by relative humidity swing 40% and 0% RH for adsorption and desorption, respectively. A cycle comprised 1 h of adsorption and 1 h of desorption and a total of 130 cycles were collected.

[0051] Cycling experiments for SCAC-1 involving exposure to light and heat comprised of a conditioning water sorption phase in a controlled environment (-40% RH and 200C) for 1 h. After adsorption, a 1 h desorption step was performed using either heating in the absence of light at 900C in an oven or via illumination with a full-spectrum lamp (exoTerra, Intense basking spot, 150 W). After a total of 10 adsorption-desorption cycles, SCAC-1 was re-analyzed.Results and discussionCharacterization of sulfonated activated carbon

[0052] A total of six sorbents for AWH based on three different commercially available activated carbons were synthesized, using either sulfuric acid or chlorosulfonic acid as sulfonation agent (Fig. 1).

[0053] The successful incorporation of sulfonic acid groups into the porous network was confirmed using Fourier-transform infrared spectroscopy (FTIR, Fig. 2). The bands at -1560 cm-1in samples AC-1, SAC-1, and SCAC-1 were assigned to stretching vibrations of aromatic carbon and the band at -1700 cnr was attributedto C=O-stretching vibrations. The appearance of additional bands at -1140 cm-1and -570 cm-1in samples SAC-1 and SCAC-1 were ascribed to S=0- and C-S- stretching, respectively. Chemical information could not be derived from the FTIR spectra of the AC-2 and AC-3 series due to the removal of most of the carbonyl functional groups, which is a well-known consequence of physicochemical activation.

[0054] XPS analysis was performed to gain an in-depth understanding of the chemical composition of functionalized and non-functionalized activated carbons. High-resolution C Is spectra (Fig. 3) reveal a wide array of functionalities. The main component observed at a binding energy of 284.8 eV is attributed to C-C bonding, comprising both sp3 and sp2 carbon. Subordinate components include C- 0 (287.1 eV), C=O (287.8 eV), O-C=O (288.6 eV), and a low intensity zz-zz * shakeup feature (290.1 eV), as well as an additional peak corresponding to C-S (286.3 eV) in sulfonated samples. The incorporation of sulfonic acid moieties was confirmed by the characteristic asymmetric shape observed in high-resolution S 2p spectra (Fig. 4) and peaks at binding energies of 168.8 eV and 169.9 eV are ascribed to S 2p3 / 2 and S 2pl / 2, respectively. Additional peaks observed at 164.0 eV and 165.3 eV in samples prepared using H2SO4 as sulfonation agent were assigned to S 2p3 / 2 and S 2pl / 2, respectively, and result from the formation of thiols in the AC backbone. The surface chemical composition determined by XPS is provided in Table 1.Table 1: Elemental composition of activated carbon (AC) and sulfonated activated carbon (SAC or SCAC) sorbents derived from XPS analysis. Sulfur content is included in both at.% and mmol-g"1.C (at.%) N (at.%) O (at.%) Cl (at.%) S (at.%) (mmol-gx)AC-1 89.28 ± 0.58 0.22 ± 10.25 ± 0.65 0.05 ± 0.20 ± 0.16 ±0.01 0.01 0.05 0.04SAC-1 77.89 ± 0.18 0.86 ± 18.20 ± 0.08 0.02 ± 3.06 ± 2.28 ±0.04 0.01 0.23 0.17SCAC-1 77.39 ± 0.21 0.67 ± 17.83 ± 0.42 0.76 ± 3.37 ± 2.48 ±0.17 0.11 0.06 0.04AC-2 91.60 ± 1.75 0.30 ± 7.65 ± 1.71 0.01 ± 0.46 ± 0.37 ±0.05 0.01 0.08 0.07SAC-2 81.88 ± 2.09 0.66 ± 14.96 ± 1.65 0.02 ± 2.49 ± 1.89 ±0.12 0.01 0.31 0.22SCAC-2 78.51 ± 0.39 0.79 ± 16.07 ± 0.84 0.74 ± 3.91 ± 2.87 ±0.18 0.16 0.11 0.08AC-3 93.13 ± 0.04 0.32 ± 5.63 ± 0.01 0.43 ± 0.50 ± 0.40 ±0.04 0.05 0.04 0.03SAC-3 77.36 ± 0.47 0.35 ± 18.44 ± 0.30 0.05 ± 3.81 ± 2.82 ±0.07 0.01 0.08 0.06SCAC-3 80.71 ± 0.13 0.53 ± 14.90 ± 0.10 0.80 ± 3.07 ± 2.29 ±0.04 0.11 0.08 0.21

[0055] Thermogravimetric analysis in air was performed to assess the thermal stability of sulfonated activated carbons (Fig. 5). Significant weight loss below 1000C was observed in all samples and is attributed to the removal of adsorbed water. Negligible degradation of all samples in air was observed up to a temperature of >2000C. The reduced stability of sulfonated activated carbons compared to their starting material is ascribed to the decomposition of sulfonic acid groups.

[0056] To gain information about the textural properties, N2 sorption isotherms were collected for all activated carbons (Fig. 6). All samples exhibited characteristics of both type I and type IVa isotherms and H3 hysteresis curves, indicative of disordered pore structures and wide pore size distribution. The presence of microporosity is evidenced by uptake at low relative pressures and mesoporosity / macroporosity was confirmed by hysteresis during desorption. The broad pore size distribution is further reflected in the values for micropore volume, VMICRO, and total pore volume, VTOT (Table 2). I ntrigu i ngly, the production of sulfonated activated carbon using sulfuric acid led to less pronounced reduction in both V MICRO and VTOT. A clear trade-off between porous properties and sulfonation could also be observed in the specific surface areas (SSABET) (Table 2). Higher sulfonation densities led to lower SSABET, for example AC-1 had 1270 m2-g - and was reduced to 823 m2-g - and 760 m2-g2in SAC-1 and SCAC-1, respectively. Table 2: S ummary of SO3H content and textural properties of activated carbon (AC) and sulfonated activated carbon (SAC or SCAC) sorbents, including BET specific surface area, SSABET, volume of micropores, VM,CR0, and total pore volume,S (mmol-g 3 SSABET(m2-g 3 VM O(cm3-g 3 VT0T(cm3-g 3AC-1 0.16 ± 0.04 1270 0.21 1.07SAC-1 2.28 ± 0.17 823 0.18 0.66SCAC-1 2.48 ± 0.04 760 0.13 0.68AC-2 0.37 ± 0.07 927 0.29 0.46SAC-2 1.89 ± 0.22 735 0.25 0.37SCAC-2 2.87 ± 0.08 472 0.15 0.26AC-3 0.40 ± 0.03 1004 0.37 0.46SAC-3 2.82 ± 0.06 175 0.10 0.14SCAC-3 2.29 ± 0.21 287 0.06 0.08Water sorption experiments

[0057] The ability of sulfonated and non-sulfonated activated carbons to absorb water directly from air was assessed by DVS. In comparison with the pristine activated carbon, the water uptake in the isotherms of sulfonated samples shifted to lower RH without detriment to the overall capacity (Fig. 7), indicating beneficial water-network interactions and confirming the role of hydrophilic sulfonate moieties. In coherence with the VToT and the specific surface area, sulfonated AC-1 materials displayed the highest water uptake, while samples based on AC-3 exhibited the lowest. Remarkably, the water adsorption capacity within the critical range <30% RH improved substantially across all samples upon sulfonation. The most notable enhancement was observed in SCAC-1, achieving an impressive water adsorption capacity of 0.16 g-g - at 30% RH and even 0.08 g-g - at 10% RH, placing it among the top performers in environments of extremely low RH.

[0058] Additional water sorption isotherms at 35 and 450C were measured for samples SAC-1 and SCAC-1 (Fig. 8), which showed that the water uptake was conserved at elevated temperatures. By applying the Clausius - Clapeyron equation to the 25 and 350C water sorption isotherms, the isosteric heat of adsorption (Qst) was calculated to be 40 kJ-mol’1and 42 kJ-mol’1for samples SAC-1 and SCAC-1, respectively, close to that of bulk water (Qst= 44 kJ-mol ).

[0059] To gain a deeper understanding of the adsorption kinetics, samples SAC-1 and SCAC-1 were exposed to 10%, 20%, 30%, and 90% RH, and the uptake monitored gravimetrically (Fig. 9). Following 5 h exposure to 10% RH, SAC-1 and SCAC-1 exhibited water sorption capacities of 0.07 g-g - and 0.08 g-g -, respectively. Remarkably, complete water uptake occurred within one hour and >90% of the total capacity was achieved within the initial 30 minutes. This rate ofuptake significantly improves upon previous examples, where reaching >90% total capacity typically took more than 2 h. Similar uptake rates were observed at 20%, 30%, and 90% RH, reaching total capacities of 0.11 g-g 0.15 g-g - and 0.65 g-g1for SAC- 1 and 0.12 g-g -, 0.16 g-g - and 0.70 g-g - for SCAC-1, respectively.

[0060] To explore the possibility of water desorption by heating, sulfonated activated carbons were first exposed to controlled conditions (-40% RH and 200C) for 24 h to allow water uptake. After conditioning, heat-induced water desorption was monitored for 1 h using a TGA at temperatures ranging from 30 to 900C (Fig. 10). In line with expectation, elevated temperatures induced accelerated water release rates, leading to a more thorough removal of the adsorbed water. The highest water release rates were observed for sulfonated activated carbons derived from AC-1, where a water removal of >80% was achieved within only 10 min at 450C. Water desorption rates could be further improved at elevated temperatures, leading to the release of >90% over the same timeframe at 600C, and almost complete desorption at 900C in both SAC-1 and SCAC-1. In TGA measurements, dry air flows over the sample, providing an additional driving force for water desorption. Given these findings in conjunction with the rapid water uptake, sulfonated activated carbons offer the potential for performing multiple adsorption-desorption cycles within short time frames, which is a vital aspect for the overall performance and economic viability of real-world AWH.Long-term stability testing

[0061] Compatible sorbents for AWH need to demonstrate stability across numerous cycles of water adsorption and desorption without detriment to the water uptake capacity. Hence, the long-term stability of the best-performing material, SCAC-1, was investigated through numerous cycles, employing either heat, simulated sunlight, or a decrease in relative humidity as trigger for desorption. By subjecting SCAC-1 to a total of 130 humidity-swings between 0 and 40% RH (Fig. 11) a reduction in the initial water uptake of <0.01 g-g1was observed, equating to a decrease in working capacity of just 2%.

[0062] Upon the completion of diverse water sorption-desorption experiments, SCAC- 1 was re-analyzed using DVS, IXL gas sorption analysis, FTIR and XPS. Water sorption isotherms at 250C after exposure to either heat or simulated sunlight displayed some reduction of water uptake capacity across the whole RH range (Fig.12). Similarly, N2sorption isotherms post-cycling (Fig. 13) revealed a slight decrease in the sorption in the meso / macropore region (>0.3 P / Po), leading to a reduction in surface area and VTOT, while VMICRO remained unaffected (Table 3). Further chemical characterization of the network, including FTIR (Fig. 14) and X- ray photoelectron spectroscopy (Table 4) revealed a slight decrease in sulfonation density, while TGA (Fig. S15) showed no detriment to the thermal stability.Table 3. Textural properties of as synthesised SCAC-1 and recovered SCAC-1, after sorption-desorption cycles using either humidity swings, simulated sunlight, or heat as desorption trigger.SCAC-1 760 0.13 0.68SCAC-l_Humidity -a-a-aSCAC-l_Light 696 0.13 0.64SCAC-l_Heat 714 0.13 0.65 a Not enough sample for determinationTable 4. Elemental composition derived from XPS analysis of as synthesisedSCAC-1 and recovered SCAC-1, after sorption-desorption cycles using either humidity swings, simulated sunlight, or heat as desorption trigger.C (at.%) N (at.%) O (at.%) Cl (at.%) S (at.%) S (mmohg ')SCAC-1 77.39 ± 0.21 0.67 ± 0.17 17.83 ± 0.42 0.76 ± 0.11 3.37 ± 0.06 2.48 ± 0.04SCAC-176.24 ± 0.16 0.72 ± 0.08 19.15 ± 0.09 0.66 ± 0.01 3.24 ± 0.04 2.38 ± 0.02HumiditySCAC-176.24 ± 0.25 0.43 ± 0.02 19.62 ± 0.31 0.71 ± 0.03 3.00 ± 0.06 2.21 ± 0.04LightSCAC-176.57 ± 0.33 0.35 ± 0.09 19.43 ± 0.28 0.65 ± 0.03 3.01 ± 0.01 2.22 ± 0.01HeatReferencesSchweng, P. et al., Small 2023, 19, 2304562(1-8)Xiao, J., et al., The Journal of Physical Chemistry C 2013, 117 (44), 23057-23065Zhu, J., et al., Environmental Science and Pollution Research 2019, 26 (16), 16166—

Claims

Claims1. A surface-modified activated carbon material comprising: activated carbon and sulfur, wherein the sulfur is comprised as sulfonate, sulfite, sulfate or sulfone groups and is present in an amount of at least 3.0 wt.%.

2. The surface-modified activated carbon material of claim 1, wherein the sulfur containing groups are covalently bound to the activated carbon.

3. The surface-modified activated carbon material of claim 1 or 2, wherein the amount of sulfur is about 3.0 to 30.0 wt.%, or about 3.0 to 25.0 wt.%, or about 3.0 to 20.0 wt.%, or about 3.5 to 20.0 wt.%, or about 4.0 to 15.0 wt.%, or about 4.5 to 10%, or about 5.0 to 6.5 wt.%4. The surface-modified activated carbon material of any one of claims 1 to 3, wherein the sulfur amount is determined by X-ray photoelectron spectroscopy (XPS) analysis.

5. The surface-modified activated carbon material of any one of claims 1 to 4, wherein the activated carbon material is a porous carbon-based material.

6. Use of the surface-modified activated carbon material of any one of claims 1 to 5 in a method of capturing water from a water containing gaseous phase or as a desiccant.

7. The use according to claim 6, wherein the water containing gaseous phase is air.

8. The use according to claim 7, wherein the relative humidity of the air is less than 100 %, 90 %, 70 %, 60 %, 50 %, 40 %, 30 %, or less than 20 %.

9. The use according to claim 6, wherein said desiccant is used for dehumidification, treatment of water damages or leaks, removal of excess water, storage in dry environments, packaging material, construction material, preservation material, drying of organic solvents, kitchen appliances, heating means, ventilation means, air conditioning systems (HVAC), as additive in construction materials, or water removal from gas streams.

10. The use according to any one of claims 6 to 9, wherein said surface-modified activated carbon material is re-used after desorption of the water.

11. A method for capturing water from a water containing gaseous phase, the method comprising the following steps:a) providing a surface-modified activated carbon material according to any one of claims 1 to 5; and b) carrying out a water sorption phase for a sufficient period of time.

12. The method of claim 11, wherein step b) is carried out for at least 1 min, or at least 2 min, or at least 3, or at least 4 min, at least 5 min, or at least 10 min, or at least 15 min, or at least 30 min, or at least 60 min.

13. The method of claim 11 or 12 further comprising a water desorption step.

14. The method of claim 13, wherein the water desorption is carried out at a temperature of between 30-2000C, or of between 40-1500C, or of between 50-1000C, or of between 60-800C.

15. The method of claim 11 to 14, wherein the desorbed water is harvested.

16. The method of claim 15, wherein the harvesting step comprises desorption, condensation and collection of the desorbed water.

17. Use of the desorbed water obtained by a method of any one of claims 13 to 16.

18. The use of claim 17, wherein the use is as drinking water19. A method for producing a surface-modified activated carbon material of any one of claims 1 to 5, comprising the following steps: a) providing an activated carbon material; b) adding a compound which comprises a sulfur moiety; c) reacting the activated carbon material and the sulfur moiety to obtain a surface-modified activated carbon material; d) collecting the surface-modified activated carbon material; e) drying the surface-modified activated carbon material; and wherein the surface-modified activated carbon comprises at least 3.0 wt % sulfur.

20. The method of claim 19, wherein the compound comprising a sulfur moiety is sulfuric acid, chlorosulfonic acid, para-toluene sulfonic acid, sulfuric anhydride, SO3, oleum, sulfamate, thionyl chloride, methane sulfonic acid, trifluoromethanesulfonic acid, trimethylsilyl sulfonic acid, metal bisulfites, or a sulfide.

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