Treatment methods of the hottest heavy metal ion w

Treatment methods of heavy metal ion wastewater and dye wastewater

porous carbon materials with complex structure composed of interconnected or closed holes not only have the advantages of carbon material properties (such as high chemical stability, good conductivity, low price, etc.), but also have the characteristics of large specific surface area. Therefore, porous carbon materials can be used in the fields of separation and purification, catalysis, optical devices, energy storage, biological separation films and nano reactors. The macroporous structure formed by three-dimensional complex structure makes porous carbon materials have excellent adsorption properties. At present, with the in-depth study of porous carbon materials, the preparation of porous carbon materials not only needs to control its mesoscopic structure, pore size and pore arrangement, but also has requirements for its micron macro morphology. Mesoporous carbon materials with various morphologies such as spheres, fibers, rods, single crystals and bulk materials have been successfully synthesized

1 types of porous carbon materials and raw materials

1.1 types of porous carbon materials

porous carbon materials according to the hole straightness, it is necessary to select the COM port to connect directly. The online diameter can be divided into microporous carbon materials (2 nm), mesoporous carbon materials (2-50 nm) and macroporous carbon materials (50 nm). Among them, microporous carbon materials are divided into extremely microporous (0.7 nm) and ultra microporous carbon materials (0.7-2 nm). Porous carbon materials can also be divided into disordered porous carbon and ordered porous carbon materials

1.2 raw materials for preparing porous carbon materials

the raw materials for preparing porous carbon materials mainly include biomass materials, synthetic polymer materials, waste polymer materials, tar and coal materials, etc. However, the structure of porous carbon prepared from different raw materials is obviously different

1.2.1 biomass materials

biomass materials that can be used as carbon material precursors include: branches, stems, leaves, fruits and shells of plants; Animal bones and feces; Marine organisms (such as algae); There are also sucrose, molasses, coffee beans, bagasse, beet residue, lignin, etc. Microporous activated carbon for adsorption of p-chlorophenol can be prepared by microwave from the seed pod of Leucaena leucocephala with an adsorption capacity of 300.6 mg/G [1]. Using rice husk ash as raw material, the specific surface area and average void of activated carbon reached 1713 m2/g and 4 nm [2]. Hayashi research group prepared porous carbon materials with K2CO3 activated carbonization of almond shell, coconut shell, walnut shell and lignin [3]. K2CO3 is also used to activate sawdust, and the report on the successful preparation of microporous carbon by microwave method [4]

1.2.2 synthetic polymer materials

synthetic polymers can control their elemental composition, molecular weight and molecular chain shape by selecting monomers and polymerization technology. Therefore, synthetic polymers can be used as both mesoporous structure directing agent and carbon material precursor. C. H. Huang et al. [5] prepared a layered porous carbon material with bagasse as template, triblock copolymer (F127) and phenolic resin as mesoporous structure directing agent and precursor, which showed good electrochemical characteristics as electrode material. Mesoporous carbon nanofibers prepared by sol-gel method with phenolic resin as precursor and F127 as template can be used for the adsorption of macromolecular dyes [6]

1.2.3 waste polymer materials

carbon containing waste comes from both synthetic polymer materials and biomass materials. Most of the wastes can be used as raw materials for the preparation of porous carbon, such as waste plastics, waste rubber and waste leather, sawdust, waste paper or pulp waste residue, urban waste and waste building materials, lampblack, distillery waste, aquatic waste, livestock waste, etc

1.2.4 tar and coal materials

tar and coal materials that can be used as carbon material precursors include peat, bituminous coal, anthracite, flue carbon black, coal tar pitch, petroleum coke, graphite, oil carbon, lignite, petroleum pitch, oil shale, etc

2 preparation methods of porous carbon materials

the preparation methods of porous carbon materials mainly include activation method and template method. The disordered porous carbon material is obtained by activation method; The porous carbon material with ordered structure and uniform pore diameter was obtained by template method. Template method is divided into soft template method, hard template method and double template method

2.1 preparation of microporous carbon materials

carbonization activation method is mainly used to prepare disordered microporous carbon. Because of its structural characteristics, biomass raw materials are more conducive to the formation of microporous carbon with high specific surface area. For example, the specific surface area of microporous activated carbon prepared with mulberry branches as carbon material precursor is 1603 m2/G [7]. Microporous carbon with large specific surface area can also be prepared with K2CO3 as activator and polyaniline as precursor [8]

molecular sieve microporous carbon is a kind of disordered microporous material, which has excellent chemical and physical stability. The main raw materials for preparing carbon molecular sieves are: polymer compounds (such as phenolic resin), coal, plants (such as coconut shell, etc.). The molecular sieve for separating ch4/n2, prepared from coal by carbonization and activation, has a specific surface area of 251 m2/G [9]. Zeolite with a pore wall of 1 nm is often used as an inorganic template for the synthesis of microporous carbon with uniform pore size. For example, microporous carbon can be synthesized by using Y-type zeolite molecular sieve as a template [10]. Kyotani team successfully synthesized microporous carbon materials with uniform pore size using Y-type zeolite molecular sieve as template [11]. Mesoporous silica template and carbon dioxide activation method can be used to prepare ordered microporous carbon with good hydrogen storage performance, and the specific surface area reaches 2008 m2/G [12]. K. S. Kim et al. [13] prepared microporous nitrogen doped carbon nanotubes with silica as template and polyaniline as precursor, which have stronger affinity for water

2.2 preparation of mesoporous carbon materials

disordered mesoporous carbon materials can be obtained by selecting appropriate carbon material precursors (such as PEG-400) and introducing mesoporous structures through chemical activation or physical activation [14]. The preparation of ordered mesoporous carbon materials mainly includes hard template and soft template methods

2.2.1 hard template method

hard template method is to immerse the carbon precursor into the template channel in liquid or gas phase, make it polymerized and crosslinked, then carbonize it, and then corrode the template with HF or NaOH solution to get ordered mesoporous carbon. The pore structure is mainly determined by the structure of the template, and its pore size can be controlled by changing the type of template or adjusting the ratio of the forebody to the template. Mesoporous silica molecular sieves (SBA-15, MCM-48) are often used as templates. For example, with SBA-15 as the template and sucrose as the carbon source, the specific surface area of the ordered mesoporous carbon material is 533-771 m2/G [15]. Sucrose, furfural alcohol and phenolic resin can be used as precursors for the preparation of ordered mesoporous carbon materials. Furfural alcohol or phenolic resin can form a rigid skeleton in the hard template, which is more conducive to maintaining the structure of mesoporous carbon. The mesoporous carbon material (CMK-1) prepared with MCM-48 as template and sucrose as carbon source has high specific surface area (1438 m2/g), large pore volume (0.98 cm3/g) and narrow pore size distribution (311 nm). CMK-1 has high adsorption capacity for bilirubin and fast adsorption speed [16]

the disadvantage of the hard template method is that there are many preparation steps, and the pore diameter is easy to shrink after the template is removed, resulting in the greatly reduced ordering of mesoporous carbon. However, silica/triblock polymer (P123) is treated with sulfuric acid and then added with sucrose. After carbonization and silicon removal, the mesoporous carbon material has good order, large specific surface area and high pore volume [17]

2.2.2 soft template method

soft template method is to use amphiphilic molecules or triblock copolymers (F127, P123 [18]) as templates, and carry out organic organic organic self-assembly with carbon material precursors in the organic phase or aqueous phase through hydrogen bonds to obtain composite nano micelles, and then cure the precursors to form a three-dimensional cross-linked rigid structure, and finally carbonize to obtain ordered mesoporous carbon materials. Taking resorcinol resin as carbon source and F127 as soft template, ordered mesoporous carbon with 3D worm like structure can be prepared [19]. Using F127, P123 and f127/p123 composites as templates and phenolic resin/hexamethylene tetramine cured product as carbon source, mesoporous carbon materials with two-dimensional hexagonal structure and worm like structure can be prepared. When F127 was used as template, the specific surface area of mesoporous carbon material reached 670 m2/G [20]. Using m-diphenol and formaldehyde as carbon sources, F127 as template and nitrate of Fe, CO and Ni as precursors, the supported ordered mesoporous carbon composites with specific surface areas of 586, 626 and 698 m2/g respectively can be obtained. This material is also easy to recover and separate [21]. Using resol phenolic resin as the precursor and F127 as the template, magnetic mesoporous carbon materials can also be prepared, but the construction industry also has mesoporous carbon materials to ensure that other goals set by the government and society are achieved [22]

2.3 preparation of macroporous carbon materials and multi-stage porous carbon materials

template method is mainly used for the synthesis of macroporous carbon materials. For example, the porous carbon material prepared with diatomite as the template is macroporous porous carbon [23]. Dong Liu et al. [24] used diatomite as a template to prepare macroporous carbon materials with a specific surface area smaller than that of commercial activated carbon, but its adsorption capacity for methylene blue is higher than that of commercial activated carbon

multistage pores can be secondary pores, such as macropores mesopores, mesopores micropores and macropores micropores, and can also be tertiary pore structures with macropores, mesopores and micropores. Multistage pore structure is more conducive to the rapid diffusion of reactants or products. Using silica opal as the macroporous template and F127 as the mesoporous template, the secondary porous carbon material was prepared. The macroporous and mesoporous diameters were about 230 and 10 nm [25]. Compared with mesoporous carbon and macroporous carbon materials, the specific surface area and porosity of secondary porous carbon materials are significantly improved

3 application of porous carbon material in wastewater treatment

porous carbon material is an adsorption material that can effectively remove organic and inorganic pollutants [26] pangolin wire is resistant to fragmentation, making it a perfect substitute. Porous carbon materials with different pore sizes have different uses. Microporous carbon materials are suitable for adsorption of small molecular compounds, while mesoporous and macroporous carbon materials are used for adsorption of dyes, vitamins and polymer compounds

3.1 treatment of heavy metal ion wastewater

mesoporous carbon materials have strong adsorption capacity for metal ions. Yin Jun et al. [27] found that the modification of elemental sulfur can introduce active sites with strong affinity for hg2++ on the surface of mesoporous carbon materials, and the adsorption capacity of hg2++ can reach 476 mg/g, with a removal rate of more than 92%. The ordered mesoporous carbon material (OMC) was synthesized with SBA-15 as template and acrylic oligomer as precursor. After being modified by ethylenediamine, the adsorption capacity of OMC for hg2++ can be doubled [28]. Chen Tian et al. [29] treated the ordered mesoporous carbon materials with oxidation, chlorination and amination to obtain aminated ordered mesoporous carbon materials, which can be used for selective adsorption of Cu (Ⅱ) and Cr (Ⅵ). The adsorption capacities of Cu (Ⅱ) and Cr (Ⅵ) before and after functionalization are 213 and 495 mg/g respectively, and 241 and 68 mg/g respectively. The specific surface area of iron doped mesoporous carbon (feomc) is 466 m2/g. When n (FE): n (c) is 5.53-7.97, the adsorption capacity of arsenic is the largest [30]

acidified mesoporous carbon foam with specific surface area of 2207 m2/g was prepared with ZnCl2 as template and fructose as carbon source. The adsorption capacity of Pb (Ⅱ) reached 188 mg/G [31]. The highly ordered mesoporous carbon material (omc-p) prepared by self-assembly with poly (ethylene oxide) -b-polystyrene block copolymer as carbon source has higher adsorption performance for Cr (Ⅵ) than the mesoporous carbon and commercial activated carbon prepared with F127 as template [32]. The porous carbon/silica gel composite prepared with sucrose as carbon source and coarse porous silica gel as template can effectively treat wastewater containing Cr (Ⅵ) [33]

3.2 treatment of dye wastewater

ordered mesoporous carbon material (CMK-3) prepared with SBA-15 as template can effectively adsorb