33 results about "Dichromate ion" patented technology

The invention discloses a high-magnetic heavy-metal ion adsorbent carrying conductive high molecules and a preparation method thereof. The adsorbent comprises high-magnetic microspheres carrying conductive high molecules, each of which comprises a Fe3O4 polycrystal sphere cluster, an amorphous SiO2 protective layer and a polypyrrole adsorption outer layer from inside to outside. The preparation method of the adsorbent is realized in a way that: carrying out a solvent thermal reduction reaction on soluble ferrites to obtain the Fe3O4 magnetic sphere cluster; carrying out the basic hydrolysis by using tetraethoxysilane to obtain the Fe3O4-SiO2 nuclear shell sphere cluster; and finally, carrying out the free radical polymerization reaction on the pyrrole monomers to obtain the Fe3O4-SiO2-polypyrrole functional particles. The heavy-metal ion adsorbent has the characteristics of stable property, high adsorption rate and reproducibility, has favorable adsorption and recovery properties on dichromic ions, and has the advantages of simple preparation process, low material price and no environmental pollution. Compared with the normal chemical absorbent, the product of the invention is convenient to use and achieves the effects of waste water treatment, pollution abatement and environment protection.

A method for producing a silicon substrate for solar cells is provided. The method includes performing a saw damage removal (SDR) and surface macro-texturing on a silicon substrate with acids solution, so that a surface of the silicon substrate becomes an irregular surface. Thereafter, a metal-activated selective oxidation is performed on the irregular surface with an aqueous solution containing an oxidant and a metal salt, in which the oxidant is one selected from persulfate ion, permanganate ion, bichromate ion, and a mixture thereof. Afterwards, the irregular surface is etched with an aqueous solution containing HF and H2O2 so as to form a nano-texturized silicon substrate.

The invention belongs to the field of fluorescence detection materials, and particularly relates to a preparation method of a rare earth terbium-based metal organic framework material and study on the performance of selectively recognizing heavy chromate ions in water. By selecting rare earth terbium emitting green light as metal central ions and selecting p-terphenyl-3,3'',5,5''-tetramethyl acid as organic sensitized ligands, a rare earth porous metal organic framework compound is synthesized under the hydrothermal condition. The compound causes the most obvious fluorescence quenching phenomenon to Cr2O72- anions in different anion solutions, and thus the compound can serve as a novel fluorescence probe for detecting Cr2O72- anions.

The invention provides a two-dimensional dinuclear zinc coordination polymer which has a simple chemical formula as shown in [Zn(HL1)L2]n.nH2O, wherein H3L1 is o-(p-carboxylbenzene)oxy-terephthalic acid, and L2 is phenanthroline. The coordination polymer is prepared through a hydrothermal method, that is, the coordination polymer is prepared by adding Zn(NO3)2.6H2O, phenanthroline, o-(p-carboxylbenzene)oxy-terephthalic acid and water in a polytetrafluoroethylene tube at a mole ratio of 2:2:1:(300 to 350), regulating the pH with 0.2 mmol / L KOH to 5, performing a reaction for 3 days in a hydrothermal reaction kettle at 413 K after stirring for 30 mins, cooling to a room temperature and then collecting white block crystals, washing with distilled water, and performing vacuum drying. The zinccoordination polymer has a two-dimensional structure with dinuclear zinc secondary structure units. The dinuclear zinc coordination polymer has a good selectivity detection to dichromate ions and chromate ions in a water solution, can be at least repeatedly used for five times or more, and can be used as a chemical sensor for efficiently detecting hexavalent chromium ions.

The invention discloses preparation of a luminescent crystal material for selectively detecting dichromate ions. The method comprises the steps of adding 4-amino-3,5-bis(imidazole methyl)-1,2,4-triazole(3-abit) and zinc acetate to an aqueous solution and stirring to obtain a stable suspension; adding 2,5-thiophenedicarboxylic acid (2,5-tdc) to the suspension and stirring to prepare a stable suspension; putting the suspension into a closed polytetrafluoroethylene reaction kettle for heating reaction, slowly cooling and then filtering, washing and drying to obtain the luminescent crystal material {[Zn(2,5-tdc)(3-abit)].H2O}n. The method has the advantage that the luminescent crystal material {[Zn(2,5-tdc)(3-abit)].H2O}n for efficiently and selectively detecting the dichromate ions is obtained.

A method for producing a silicon substrate for solar cells is provided. The method includes performing a saw damage removal (SDR) and surface macro-texturing on a silicon substrate with acids solution, so that a surface of the silicon substrate becomes an irregular surface. Thereafter, a metal-activated selective oxidation is performed on the irregular surface with an aqueous solution containing an oxidant and a metal salt, in which the oxidant is one selected from persulfate ion, permanganate ion, bichromate ion, and a mixture thereof. Afterwards, the irregular surface is etched with an aqueous solution containing HF and H2O2 so as to form a nano-texturized silicon substrate.

The invention relates to a cellulose-based multifunctional absorbing material and preparation and application methods thereof. The preparation method comprises performing TEMPO (tetramethylpiperidine-1-oxyl) oxidation / NaIO4 oxidation or NaIO4 oxidation / TEMPO oxidation sequentially on cellulose-based materials such as cotton cloth, gauze linen, and then performing further surface grafting modification to obtain a multifunctional absorbing fabric in a submicrometer and nanometer structure. The multifunctional absorbing fabric contains special functional groups such as carboxyl, aldehyde, amido,sulfydryl, sulfon, cyan and acylamino and can be applied to the fields of absorbing heavy metal ions such as lead ions and dichromic ions in polluted water, dyes such as methylene blue and acid yellow, ethyl alcohol in yellow rice wine to reduce alcoholic strength and the like.

The invention discloses an Ag-MOFs metal organic framework material, a synthesis method thereof and application thereof in ion identification. A chemical molecular formula of the metal organic framework material is {[Ag(H2L)]}n, and L is an organic ligand 4-(2,4,6-carboxyl phenyl)-2,2':6',2'- terpyridyl. A proton is removed from one carboxyl, and adjacent silver ions are bridged to form a wave-form 1D chain-shaped structure. A 1D ladder-shaped chain is connected with other 1D ladder-shaped chains through hydrogen bonds, so that a 2D layered structure is further expanded. The material is simpleto prepare, is novel in structure, and is stable in an aqueous solution, and trivalent iron ions and heavy chromium acid radical ions can be quickly detected.

The invention discloses a synthesis method and an application of Tb<3+>-modified Al-BTC nanotubes. A tubular Al-BTC nanostructure is fast synthesized at room temperature through using a direct precipitation technology with soluble aluminum salt as a metal source and basic salt of 1,3,5-benzenetricarboxylic acid (1,3,5-BTC) as an organic ligand, and the nanotubular morphology of the above obtained product has not yet been reported in literatures. The method has the advantages of no need of other additives or templates in the reaction, no need of too high temperature or strict device requirements, short time, and non-strict reaction environment requirements. An Al-BTC / Tb fluorescent material is obtained after room temperature post-treatment of the Al-BTC nanotubes, and the Al-BTC / Tb fluorescent material has a good fluorescence quenching effect on cations iron ions and anions dichromate radicals, can be used to simply and fast carry out qualitative detection of above ions, and also can realize quantitative detection of ferric iron ions in a low concentration range.

The invention belongs to the technical field of applications of fluorescence carbon nano-materials, and concretely relates to a preparation method of carbon quantum dots, and a method for detecting dichromate ions by using the carbon quantum dots. The green preparation of the carbon quantum dots is carried out by using cheap and easily available phosphoric acid or water-soluble phosphate and organic amine as raw materials without a surface passivating agent or other additives in order to prepare the N,P-doped carbon quantum dots having a good water solubility, the carbon quantum dots have uniformly distributed particle sizes, and the average diameter of carbon quantum dot particles is not more than 5 nm. The preparation method has the advantages of cheap raw materials, simplicity and fastness, the selective detection of Cr<2>O<7><2-> is realized by the quantum dots, the detection limit of the quantum dots to Cr<2>O<7><2-> is low, the lowest detection limit can reach 1.2 [mu]M, and highly sensitive detection is achieved. The detection method is not affected by most interference ions (such as Cu<2+>, K<+>, Na<+>, Ca<2+>, Mg<2+>, Co<2+>, Ni<2+>, Ba<2+>, Pb<2+>, Fe<2+>, Zn<2+>, Al<3+>and Fe<3+>, and has a great application prospect.

The invention discloses a Cd(II) metal organic framework material based on 5-(4-[1,2,4]triazole-1-phenyl)-1H-tetrazole, a preparation method and application thereof. The metal organic framework material is prepared by taking 5-(4-[1,2,4]triazole-1-phenyl)-1H-tetrazole and CdCl2.2.5H2O as raw materials througha solvothermal method; the molecular formula of the metal organic framework is [Cd(L)2(H2O)2]n, wherein L is a ligand 5-(4-[1,2,4]triazole-1-phenyl)-1H-tetrazole; and when the metal organic framework material is used for the detection of nitrobenzene (NB), acetone (ACE), iron ions (Fe<3+>)and dichromate ions (Cr2O7<2->) as a fluorescent sensing material, high sensitivity is shown.

The invention discloses a novel and efficient composite adsorbing material obtained by loading crab shell powder on granular porous ceramsites, which belongs to the field of water treatment. The invention also discloses a method of using the granular porous ceramsites loaded with the crab shell powder to remove the heavy chromate in water, i.e., using the granular porous ceramsites loaded with the crab shell powder to adsorb and remove the heavy chromate ions in the water under a neutral condition. According to the invention, the heavy chromate ions in the water are removed by an adsorption process, but the removal and recycling and reusing effects of the composite adsorbing material are obviously superior to those of the traditional adsorbing material. In addition, the invention has the advantages that the operation is simple, the materials are easy to obtain, the cost is low, the recycling rate is large, the regeneration is realized, and no secondary pollution is caused. Therefore, the composite adsorbing material for removing the heavy chromate in the water, provided by the invention, can be used for removing the heavy chromate ions in waste water, and has good economic and environmental benefits.

The invention discloses a recovery and comprehensive utilization process for electroplating wastewater. The process includes the following steps of firstly, regulating the pH value of electroplating wastewater to 2-3; secondly, adding a reducing agent to reduce dichromate ions or chromate ions in water into trivalent chromium; thirdly, regulating the pH value of electroplating wastewater to 8.5-9.0 to form sediment, and conducting filtration; fourthly, drying sediment, and determining a chromic hydroxide product with the chromium content of 25-45% through the titrimetry method; fifthly, dissolving the product through sulfuric acid to generate chromium sulfate, and conducting concentration and evaporation to form a crude product. By means of the recovery and comprehensive utilization process for electroplating wastewater, chromium salt can be recovered from chromium-containing wastewater, and discharged water can reach the emission standard.

The invention discloses a novel method for repairing heavy metal cadmium, arsenic, mercury, lead and chromium combined polluted soil, and relates to the technical field of soil repairing. The inventor improves the remediation material and method for the heavy metal compound contaminated soil, soil acidification is accelerated through an acidification material and a first passivation material, arsenic passivation fixation and dichromate ion reduction are conducted through acidification and oxidation-reduction reaction in the acidification process, meanwhile, release of adsorbed chromium, cadmium, mercury and lead is accelerated, and the remediation effect of the heavy metal compound contaminated soil is improved. And then a soil pH increasing material and a second passivation material are added, so that cadmium, mercury, lead and chromium cations are rapidly and completely passivated, and the two-step operation can realize complete fixation of cadmium, arsenic, mercury, lead and chromium pollution elements in the polluted soil and thorough remediation.

The invention provides a terbium diphenylamine carbonyl benzoic acid rare earth complex, which is synthesized by taking 2-diphenylamine carbonyl benzoic acid and terbium nitrate as raw materials through water bath heating and a one-pot method. The preparation method has the advantages of simple synthesis process, low cost, easy control of chemical components, good repeatability, high yield and the like. The terbium diphenylamine carbonyl benzoic acid rare earth complex is good in fluorescence intensity and monochromaticity, and under a three-purpose ultraviolet lamp, when the excitation wavelength is 254 nm, the material emits strong green fluorescence. The terbium diphenylamine carbonyl benzoic acid rare earth complex can be used as a fluorescent probe to identify dichromate ions (Cr2O7<2->) harmful to the environment, and has high selectivity.

The invention provides a preparation method of a cadmium metal complex and applications of the cadmium metal complex as a fluorescent probe and a photodegradation catalyst. The chemical formula of thecomplex is [Cd4(L)3(DMF)Cl2.H2O]n, wherein H2L is 1,1'-(4-carboxylphenyl)-2,2'-biimidazole. The cadmium metal complex is of a three-dimensional structure formed by self-assembling cadmium ions with an L<2-> ligand. The cadmium complex has an obvious fluorescence quenching effect on ferric ions, dichromate ions, antibiotics furacilin and nitrofurantoin, can be used as the fluorescent probe, and has potential application values in the fields of environmental monitoring and life science. In addition, the cadmium complex has stable and efficient catalytic photodegradation dye properties, makes methylene blue basically completely degraded within 100 minutes under the condition of visible light, is easy to separate and can be recycled for multiple times.

The invention provides a preparation method of a cadmium metal complex and an application of the cadmium metal complex as a fluorescent probe and a photodegradation catalyst. The chemical formula of the complex is [Cd(L)(H2O).5H2O]n, wherein H2L is 1,1'-(4-carboxylphenyl)-2,2'-biimidazole. The cadmium metal complex is of a three-dimensional structure formed by self-assembling cadmium ions with anL<2-> ligand. The cadmium complex has an obvious fluorescence quenching effect on ferric ions, dichromate ions and antibiotics furacilin and nitrofurantoin, can be used as the fluorescent probe, and has potential application values in the fields of environmental monitoring and life science. In addition, the cadmium complex has stable and efficient catalytic photodegradation dye properties: methylene blue, methyl orange and rhodamine B are basically and completely degraded within 60 min under the condition of visible light, and the cadmium complex is easy to separate and can be recycled for multiple times.

The invention provides a method for removing dichromate ions in wastewater by adsorption based on calcium-iron binary hydrotalcite serving as an adsorbent, wherein the ratio of calcium to iron is (2-4):1. The weight of the dichromate ions adsorbed by the calcium-iron binary hydrotalcite can reach (141-562)mg / g. The method comprises the steps: adding the adsorbent into a wastewater solution containing the dichromate ions under the condition of room temperature according to a proportion that the mass ratio of the adsorbent to the dichromate ions contained by wastewater is (0.3-6):1, and carryingout stirring for 1h to realize adsorption balance. The method has the advantages of simple process, operation simplicity and high efficiency-cost ratio and shows a huge application potential and a relatively high economic value.

The invention provides a preparation method of a zinc metal complex, and applications of the zinc metal complex as a fluorescent probe and a ferroelectric material. The chemical formula of the complexis [Zn(L).H2O] n, wherein H2L is 1,1'-(4-carboxyl phenyl)-2,2'-biimidazole. The zinc metal complex is of a three-dimensional structure formed by self-assembling zinc ions with an L<2-> ligand. The zinc complex shows an obvious fluorescence quenching effect on ferric ions, dichromate ions, antibiotics furacilin and nitrofurantoin, can be used as the fluorescent probe, and has potential applicationvalues in the fields of environmental monitoring and life science. In addition, the zinc complex has excellent ferroelectric properties: when an external electric field is 1200 V, the remnant polarization is 1.84 [mu]C / cm<2>, the coercive field is 714 V / cm, and the saturation polarization is 2.15 [mu]C / cm<2>, so that the zinc complex is expected to become the novel ferroelectric material, and hasa wide application prospect in the field of information storage.

The invention discloses a 5-isonicotinamidopyridylisotitanate cadmium complex, and a preparation method and an application thereof, and belongs to the technical field of porous layered materials. Theporous complex has a two-dimensional double-layer network structure, the chemical expression of the porous complex is [Cd2(L)2DMFTHF].2DMF.THF, wherein L is a 5-isonicotinamidopyridylisotitanate ion.The preparation method comprises the following steps: carrying out a solvothermal reaction on 5-isonicotinamidopyridylisotitanic acid and a cadmium salt, and washing and drying the obtained reaction product to obtain the novel porous cadmium complex with a stable structure. The preparation method has the advantages of simple process, convenience in operation, and high yield; and the prepared 5-isonicotinamidopyridylisotitanate cadmium complex can selectively catalyze a Knoevenagel condensation reaction of p-tolualdehyde and malononitrile, has the characteristics of good selectivity and high catalytic activity as a catalyst, and can be used as a fluorescent probe for dichromate ions and permanganate ions.

The invention provides a two-dimensional dinuclear zinc coordination polymer which has a simple chemical formula as shown in [Zn(HL1)L2]n.nH2O, wherein H3L1 is o-(p-carboxylbenzene)oxy-terephthalic acid, and L2 is phenanthroline. The coordination polymer is prepared through a hydrothermal method, that is, the coordination polymer is prepared by adding Zn(NO3)2.6H2O, phenanthroline, o-(p-carboxylbenzene)oxy-terephthalic acid and water in a polytetrafluoroethylene tube at a mole ratio of 2:2:1:(300 to 350), regulating the pH with 0.2 mmol / L KOH to 5, performing a reaction for 3 days in a hydrothermal reaction kettle at 413 K after stirring for 30 mins, cooling to a room temperature and then collecting white block crystals, washing with distilled water, and performing vacuum drying. The zinccoordination polymer has a two-dimensional structure with dinuclear zinc secondary structure units. The dinuclear zinc coordination polymer has a good selectivity detection to dichromate ions and chromate ions in a water solution, can be at least repeatedly used for five times or more, and can be used as a chemical sensor for efficiently detecting hexavalent chromium ions.

The invention provides an inorganic hybrid probe as well as a preparation method and application thereof, the inorganic hybrid probe comprises a rare earth organic complex, and the rare earth organic complex is covalently bound with a silanized layered mineral. By means of the method, the problem of insufficient thermal stability of the rare earth organic complex is solved, a convenient and feasible method is provided for detecting copper ions and dichromate ions, and the corresponding fluorescence spectrum detection limits are 13nM and 38nM respectively.

The invention discloses a synthesis method and an application of Tb<3+>-modified Al-BTC nanotubes. A tubular Al-BTC nanostructure is fast synthesized at room temperature through using a direct precipitation technology with soluble aluminum salt as a metal source and basic salt of 1,3,5-benzenetricarboxylic acid (1,3,5-BTC) as an organic ligand, and the nanotubular morphology of the above obtained product has not yet been reported in literatures. The method has the advantages of no need of other additives or templates in the reaction, no need of too high temperature or strict device requirements, short time, and non-strict reaction environment requirements. An Al-BTC / Tb fluorescent material is obtained after room temperature post-treatment of the Al-BTC nanotubes, and the Al-BTC / Tb fluorescent material has a good fluorescence quenching effect on cations iron ions and anions dichromate radicals, can be used to simply and fast carry out qualitative detection of above ions, and also can realize quantitative detection of ferric iron ions in a low concentration range.

The invention discloses an Ag-MOFs metal organic framework material, a synthesis method thereof and application thereof in ion identification. A chemical molecular formula of the metal organic framework material is {[Ag(H2L)]}n, and L is an organic ligand 4-(2,4,6-carboxyl phenyl)-2,2':6',2'- terpyridyl. A proton is removed from one carboxyl, and adjacent silver ions are bridged to form a wave-form 1D chain-shaped structure. A 1D ladder-shaped chain is connected with other 1D ladder-shaped chains through hydrogen bonds, so that a 2D layered structure is further expanded. The material is simpleto prepare, is novel in structure, and is stable in an aqueous solution, and trivalent iron ions and heavy chromium acid radical ions can be quickly detected.

The invention belongs to the field of fluorescence detection materials, and particularly relates to a preparation method of a rare earth terbium-based metal organic framework material and study on the performance of selectively recognizing heavy chromate ions in water. By selecting rare earth terbium emitting green light as metal central ions and selecting p-terphenyl-3,3'',5,5''-tetramethyl acid as organic sensitized ligands, a rare earth porous metal organic framework compound is synthesized under the hydrothermal condition. The compound causes the most obvious fluorescence quenching phenomenon to Cr2O72- anions in different anion solutions, and thus the compound can serve as a novel fluorescence probe for detecting Cr2O72- anions.

The invention discloses a rare earth material based on diphenylamine carbonyl benzoic acid. The structural formula of the rare earth material is shown in the specification, and R in the formula is a water molecule. The invention also provides a preparation method and application of the rare earth material based on diphenylamine carbonyl benzoic acid. The rare earth material has the beneficial effects that the rare earth material based on diphenylamine carbonyl benzoic acid can be used as a fluorescent probe for identifying dichromate ions (Cr2O7<2->) harmful to the environment, and has high selectivity; and the yield of the rare earth material based on diphenylamine carbonyl benzoic acid prepared by the method is high.

The invention provides a preparation method of a cobalt metal complex, and applications of the cobalt metal complex as a fluorescent probe and a ferroelectric material. The molecular formula of the complex is [Co(AIP)(TMIB)0.5.4H2O]n, wherein H2AIP is 5-aminoisophthalic acid, and TMIB is 1,3,5-tri(2-methyl-1-imidazolyl)benzene. The cobalt complex is of a two-dimensional network structure formed byself-assembling cobalt ions with AIP<2-> and TMIB ligands. The cobalt complex has an obvious fluorescence quenching effect on ferric ions and dichromate ions, can be used as the fluorescent probe, and has potential application values in the fields of environmental monitoring and life science. In addition, the cobalt complex has excellent ferroelectric properties: when an external electric field is 800 V, the residual polarization Pr is 0.936 [mu]C / cm<2>, the coercive field Ec is 352 V / cm, and the saturated polarization Ps is 1.123 [mu]C / cm<2>, so that the cobalt complex is expected to becomethe novel ferroelectric material and has a wide application prospect in the field of information storage.

The invention belongs to the technical field of applications of fluorescence carbon nano-materials, and concretely relates to a preparation method of carbon quantum dots, and a method for detecting dichromate ions by using the carbon quantum dots. The green preparation of the carbon quantum dots is carried out by using cheap and easily available phosphoric acid or water-soluble phosphate and organic amine as raw materials without a surface passivating agent or other additives in order to prepare the N,P-doped carbon quantum dots having a good water solubility, the carbon quantum dots have uniformly distributed particle sizes, and the average diameter of carbon quantum dot particles is not more than 5 nm. The preparation method has the advantages of cheap raw materials, simplicity and fastness, the selective detection of Cr<2>O<7><2-> is realized by the quantum dots, the detection limit of the quantum dots to Cr<2>O<7><2-> is low, the lowest detection limit can reach 1.2 [mu]M, and highly sensitive detection is achieved. The detection method is not affected by most interference ions (such as Cu<2+>, K<+>, Na<+>, Ca<2+>, Mg<2+>, Co<2+>, Ni<2+>, Ba<2+>, Pb<2+>, Fe<2+>, Zn<2+>, Al<3+>and Fe<3+>, and has a great application prospect.

The invention discloses an etching solution and an etching method. The etching solution comprises nitric acid or phosphoric acid, a buffering agent, a permanganate ionic compound or dichromate ionic compound, or a mixture of the permanganate ionic compound and the dichromate ionic compound; each litre of etching solution comprises 85-110g / L of nitric acid, 0.2-2.0g / L of buffering agent and 60-90g / L of permanganate ionic compound; or each litre of etching solution comprises 85-110g / L of nitric acid, 0.2-2.0g / L of buffering agent and 140-165g / L of dichromate ionic compound. The etching method comprises the following steps of: carrying mechanical polishing on a CdZnTe substrate on which a HgCdTe film grows, so that the remaining HgCdTe is 15-25 micrometers; and then putting the CdZnTe substrate into the etching solution to carry out etching, and cleaning the etched CdZnTe substrate by using absolute ethyl alcohol to obtain the HgCdTe film. The etching solution disclosed by the invention can be used for effectively etching the CdZnTe substrate under the HgCdTe film and has little influence on the HgCdTe film.

The invention provides a preparation method of a zinc complex and an application of the zinc complex as a fluorescent probe and a photodegradation and ferroelectric material. The chemical formula of the complex is [Zn(1,3-BMIB)(TBIP).2H2O]n, wherein 1,3-BMIB is 1,3-bis(2-methyl-1-imidazolyl)benzene, and H2TBIP is 5-tert-butylisophthalic acid. The zinc complex is of a three-dimensional structure formed by self-assembling of Zn<2+> with 1,3-BMIB and TBIP<2-> ligands. The zinc complex has an obvious fluorescence quenching effect on ferric ions, dichromate ions and furacilin, can be used as the fluorescent probe, and has potential application values in the fields of environmental monitoring and life science. The zinc complex has the property of efficiently catalyzing and degrading methylene blue dye, is easy to separate and can be recycled for multiple times. The zinc complex has excellent ferroelectric properties, is expected to become a novel ferroelectric material and has a wide application prospect in the field of information storage.