Preparation of bio-based porous carbon by microwave assisted phosphoric acid activation and its use for adsorption of Cr(VI)

Simultaneous removal of aqueous same ionic type heavy metals and dyes by a magnetic chitosan/polyethyleneimine embedded hydrophobic sodium alginate composite: Performance, interaction and mechanism

Heavy metals and azo dyes caused huge harm to the aqueous system and human health. A magnetic chitosan/polyethyleneimine embedded hydrophobic sodium alginate composite (MCPS) was designed and prepared to simultaneously remove aqueous same ionic type heavy metals and azo dyes. In mono-polluted system, the optimal pH for Cr(VI), MO (methyl orange), Cu(Ⅱ) and MB (methylene blue) were 3, 2, 6 and 12 with a saturated adsorption capacity of 87.53, 66.41, 351.03 and 286.54 mg/g, respectively. Pseudo-second-order was suitable to describe the adsorption kinetics of them and the adsorption isotherms were more consistent with the Langmuir isotherm model being a spontaneous, endothermic, and entropy-increasing process. In binary-polluted system, MCPS possessed simultaneous adsorption for Cr (Ⅵ)-MO and Cu(Ⅱ)-MB pollutants at their optimal pH, in addition, whether in anionic or cationic solution, the removal of heavy metals were promoted with the add of azo dyes but the removal of azo dyes were suppressed with the add of heavy metals. Both Cr (Ⅵ)-MO and Cu(Ⅱ)-MB pollutants could be effectively adsorbed and desorbed from MCPS by changing the pH of the aqueous solution to realize recyclability. Lastly, removal mechanism was revealed in detail by FT-IR, EDS and XPS.

Effects of different exogenous cadmium compounds on the chemical composition and adsorption properties of two gram-negative bacterial EPS

Three different Cd(II) compounds were used to regulate Pseudomonas aeruginosa and Alcaligenes faecalis EPS (extracellular polymeric substances). The purpose of this study was to improve the content of EPS protein and the adsorption capacity of Cd(II) by different Cd(II) compounds. The results showed that Cd(NO₃)₂ had the best stress/induction effect on the two strains. Under the best stress/induction, the protein in EPS of the two strains increased most obviously, and the adsorption capacity of Cd(II) was increased by more than 40%. Under these conditions, the kinetics of the adsorption process of Cd(II) by Cd(NO₃)₂-EPS_{A. F} (EPS produced by Alcaligenes faecalis under Cd(NO₃)₂ stress) could be well fitted by the Langmuir isotherm model, and the theoretical maximum adsorption amount of 1111.11 mg/g EPS could be obtained. The results of 3D-EEM, FTIR and XPS indicated that proteins, especially CO, CN and NH in proteins, played a major role in the removal of Cd(II) by Cd(NO₃)₂-EPS_{A. F}. The results of this study show that the addition of Cd(NO₃)₂ can effectively regulate the content of chemical components, especially the content of protein, and thus greatly improve the removal efficiency of heavy metals, which shows great application prospects in the prevention and control of heavy metal pollution.

Preparation and evaluation of activated carbon from low-rank coal via alkali activation and its fundamental CO2 adsorption capacity at ambient temperature under pure pressurized CO2

The relationship between the CO2 adsorbed amount and specific surface area (a) or pore volumes (b) of the prepared activated carbon. The open plot is the prepared activated carbon. The solid plot is the activated carbon prepared from BN, TN, and SO.

Synthesis of Mg-Al Hydrotalcite Clay with High Adsorption Capacity

A novel Mg-Al metal oxide has been successfully synthesized by the calcination of hierarchical porous Mg-Al hydrotalcite clay obtained by using filter paper as a template under hydrothermal conditions. Various characterizations of the obtained nanoscale oxide particles verified the uniform dispersion of Mg-Al metal oxides on the filter paper fiber, which had a size of 2–20 nm and a highest specific surface area (SSA) of 178.84 m²/g. Structural characterization revealed that the as-prepared Mg-Al metal oxides preserved the tubular morphology of the filter paper fibers. Further experiments showed that the as-synthesized Mg-Al metal oxides, present at concentrations of 0.3 g/L, could efficiently remove sulfonated lignite from oilfield wastewater (initial concentration of 200 mg/L) in a neutral environment (pH = 7) at a temperature of 298 K. An investigation of the reaction kinetics found that the adsorption process of sulfonated lignite (SL) on biomorphic Mg-Al metal oxides fits a Langmuir adsorption model and pseudo-second-order rate equation. Thermodynamic calculations propose that the adsorption of sulfonated lignite was spontaneous, endothermic, and a thermodynamically feasible process.

Fabrication and Characterization of Activated Carbon Fibers from Oil Palm Trunk

To develop more valuable application, oil palm trunk was successfully converted into activated carbon fibers (ACFs). An effective process of chemical treatment with dilute sulfuric acid was conducted to improve the thermal stability of primary fibers for further heating treatment. Carbon dioxide (CO2) was used as activator to produce much porous structure with various pore diameter. The specific surface area (SBET) and total pore volume (Vtotal) of resultant ACFs showed increasing trend as rise of activation temperature and time. The ACFs obtained under the temperature of 900 °C and time of 90 min exhibited highest SBET and Vtotal, which were more than 1800 m2/g and 0.7 mL/g, respectively. Meanwhile, more graphic carbon on the surface of ACFs were destroyed with prolonging activation time, resulting in the oxygen-containing functional groups formed during activation process with CO2. Due to the abundant pores and surface functional groups, the ACFs exhibited excellent adsorption capacity of chromium and would be an alternative material for industrial adsorption utilization.

Characterization and comparison of walnut shells-based activated carbons and their adsorptive properties

The production of low-cost biologically activated carbons (BACs) is urgent need of environmental protection and ecological sustainability. Hence, walnut shells were treated by traditional pyrolysis, direct KOH impregnation and combined activation composed of hydrothermal carbonization and two-step H3PO4- and pyrolysis-activation process to obtain porous carbon with high adsorption capacity. It was found that the best adsorption capacity for iodine and organic dye methylene blue (MB) can be obtained using the KOH impregnation at impregnation ratio of 1:1 or combined activation comprising of 2 h H3PO4 activation and 1 h pyrolysis activation at 1000°C. The produced KOH, H3PO4/pyrolysis activated BACs at the optimum conditions are superior to that of commercial ACs, 9.4 and 1.3 times for MB removal, 4 and 4.5 times for iodine number respectively. Characterization results demonstrated their porous structure with very good textural properties such as high BET surface area (1689.1 m2/g, 1545.3 m2/g) and high total pore volume (0.94 cm3/g, 0.96 cm3/g). The N2 adsorption-desorption isotherm of H3PO4/pyrolysis activated hydrochar suggested the co-existence of micro and meso-pores. Moreover, they are more effective for the removal of Fe(III) and Cr(VI) from aqueous solution than the commercial AC, suggesting a promising application in the field of water treatment.

Carbon material-immobilized ionic liquids were applied on absorption of Hg2+ from water phase

In this study, several immobilized ionic liquid adsorbents on carbon materials were synthesized with impregnation method. The carrier materials were activated carbon and three kinds of multi-walled carbon nanotubes. And the synthetic adsorbents immobilized different kinds of ionic liquids were characterized by Boehm titration, FT-IR, XPS, TG, and BET analysis, respectively. Finally, carbon materials after [C4mim]HSO₄ immobilization were selected as adsorbent to remove Hg²⁺ from water phase. The optimum conditions of adsorption test of ionic liquid immobilized by multi-walled carbon nanotubes were as follows: the initial concentration of Hg²⁺ was 400 mg/L, the adsorbent addition amount was 40 mg, the temperature was 20 °C, the reaction time was 200 min, the removal rate of Hg²⁺ peaked at 62.95%, the adsorption capacity was reached 79.00 mg/g. The optimum conditions of adsorption test of ionic liquid immobilized by activated carbon were as follows: the initial concentration of Hg²⁺ was 300 mg/L, the adsorbent addition amount was 0.2 g, the temperature was 20 °C, pH was 2.0, the reaction time was 100 min, the removal rate of Hg²⁺ was more than 99%, the adsorption capacity was 118.65 mg/g. The adsorption isotherm fitting study found that the adsorption of adsorbent on Hg²⁺ was more in line with the Langmuir model, and the adsorption kinetics study shows that the adsorption process is consistent with the pseudo-second-order kinetic equation. The results of kinetic analysis are further verified by thermodynamic analysis.

Removal of ciprofloxacin from aqueous solution by rabbit manure biochar

Biochar was prepared from rabbit faeces at 400°C, 500°C, 600°C, and 700°C, respectively (labelled RFB₄₀₀, RFB₅₀₀, RFB₆₀₀, and RFB₇₀₀, respectively), and was characterized by elemental analysis, BET, SEM and FTIR. The adsorption factors, kinetics, isothermal adsorption and thermodynamics of the adsorption properties were investigated in batch experiments. The results showed that RFB possessed a large specific surface area and was rich in pore structure, and the aromaticity and stability increased with the pyrolysis temperature of the biochar. When the solution pH was 11, adsorption achieved equilibrium at approximately 180 min. The kinetic data were well-represented by the pseudo-second-order model, indicating that the adsorption rate was jointly controlled by liquid film diffusion, surface adsorption and intra-particle diffusion. The results of isothermal adsorption and thermodynamics showed that the adsorption behaviour of CIP (ciprofloxacin) onto RFB was better fitted with the Langmuir model, and the adsorption process was spontaneous and endothermic. FTIR studies showed that RFB was rich in oxygen-containing functional groups and that hydrogen bonds and π-π bonds were closely related to the adsorption process. This work showed that the rabbit faeces-derived biochar has promise as an effective adsorbent to remove ciprofloxacin from wastewater.

Synthesis of hierarchical MgO based on a cotton template and its adsorption properties for efficient treatment of oilfield wastewater

A biomorphic MgO nanomaterial was fabricated via a facile and low-cost immersion method using cotton as the template.

Intelligent-activated carbon prepared from pistachio shells precursor for effective adsorption of heavy metals from industrial waste of copper mine

A novel and efficient bio-adsorbent based on magnetic activated carbon nanocomposites (MAC NCs)-modified by sulfamic acid (H₃NSO₃) has been developed from pistachio shell precursor as agricultural by-products and then was applied for heavy metal removal. Design an experimental model (Central Composite Design (CCD)) for adopting surface response could efficiently be used for adsorption process, and it is an economical way of obtaining the optimal adsorption conditions based on the limited number of experiments. The variants of adsorbent dosage, metal ion concentration, and contact time were optimized for Cu(II) metal by CCD. In addition, adsorption capacity and isoelectric point (pHzpc) of adsorbent were studied at different pH values. Kinetic and isotherm of adsorption were investigated via the Langmuir and the pseudo-second-order model. The maximum adsorption capacity using the Langmuir model was 277.77 mg g^-1 for Cu(II) ions on H₂NSO₃-MAC NCs. Then adsorption process was investigated for ions of Fe(II), Zn(II), and Ni(II) under optimized condition. Also, the competitive adsorption of Fe(II), Zn(II), and Ni(II) ions mixed solution onto H₂NSO₃-MAC NCs was conducted. Adsorption-desorption results exhibited that the H₂NSO₃-MAC NCs can be used up to seven cycles while they have excellent performance. Finally, to evaluate the efficiency of this bio-adsorbent, the removal of heavy metals from wastewater of the Sarcheshmeh copper mine as a real sample was studied. Graphical abstract.

Characterization and Preparation of Nano-porous Carbon Derived from Hemp Stems as Anode for Lithium-Ion Batteries

As a biomass waste, hemp stems have the advantages of low cost and abundance, and it is regarded as a promising anode material with a high specific capacity. In this paper, activated carbon derived from hemp stems is prepared by low-temperature carbonization and high-temperature activation. The results of characterizations show the activated carbon has more pores due to the advantages of natural porous structure of hemp stem. The aperture size is mainly microporous, and there are mesopores and macropores in the porous carbon. The porous carbon has an excellent reversible capacity of 495 mAh/g after 100 cycles at 0.2 °C as the anode of lithium-ion battery. Compared with the graphite electrode, the electrochemical property of activated carbon is significantly improved due to the reasonable distribution of pore size. The preparation of the activated carbon provides a new idea for low cost and rapid preparation of anode materials for high capacity lithium-ion batteries.

Hexavalent chromium adsorption on virgin, biochar, and chemically modified carbons prepared from Phanera vahlii fruit biomass: equilibrium, kinetics, and thermodynamics approach

A novel biosorbent Phanera vahlii fruit biomass (PVF) and its biochar and chemically modified forms were studied for the elimination of Cr(VI) from synthetic solutions. Biosorbents were characterized through BET, FTIR, FESEM, EDX, and TGA technique. The parameters influencing biosorption were optimized and found as pH 2.0, temperature 303 K, initial metal concentration 500 mg/L, and biosorbent dosage 0.5 g/L. The ideal contact time was 180 min for all biosorbents. Freundlich isotherm was found to have good correlation with investigational data, which indicated that biosorption takes place in multiple layer style. Langmuir adsorption isotherm yielded the highest biosorption capacity (Q_o) to be 159.1, 225.1, 244.1, and 278.5 mg/g for Phanera vahlii fruit biomass, Phanera vahlii biochar, Phanera vahlii phosphoric acid activated carbon, and Phanera vahlii zinc chloride activated carbon, respectively. Experimental data had good correlation with pseudo-second-order kinetic model fitted. Thermodynamic studies indicated the biosorption process to be spontaneous, stable, and endothermic. Thus, it was concluded that Phanera vahlii fruit biomass and the derived activated carbons are promising biosorbents for adsorption of chromium from aqueous solutions. Graphical abstract.

Removal of heavy metals from aqueous solution using chitosan-combined magnetic biochars

The use of chitosan combined with magnetic Loofah biochar (CMLB) was investigated for the removal of Cr(VI) and Cu(II) from aqueous solution. The modified biochar had higher Cr(VI) and Cu(II) adsorption capacity than that of pristine biochar. 40%-CMLB showed high Cr(VI) and Cu(II) adsorption capacity of 30.14 mg/g, and 54.68 mg/g, respectively. Adsorption reached equilibrium within 18 h. The study found that the experimental data showed the best fit for the pseudo-second-order kinetic model and Freundlich model. Additionally, after three reuse cycles, Cr(VI) and Cu(II) adsorption capacity by CMLB were 23.34 mg/g and 42.6 mg/g, respectively. XPS results indicated that ion exchange and surface complexation were the primary mechanisms for Cr(VI) and Cu(II) adsorption.

Preparation, adsorptive properties and chemical regeneration studies of high-porous activated carbon derived from Platanus orientalis leaves for Cr(VI) removal

Activated carbon (AC) was prepared from Platanus orientalis leaves by H₃PO₄ activation using a microwave heating method and characterized by SEM (scanning electron microscopy), Brunauer-Emmett-Teller (BET) surface area analysis and FTIR (Fourier transform infrared spectroscopy) techniques. AC exhibited a surface area of 1089.67 m²/g and a relatively high pore volume of 1.468 cm³/g. Utilization of AC for the removal of Cr(VI) from aqueous solution was researched. The adsorption efficiency was highly pH dependent and adsorption capacity of AC for Cr(VI) could reach up to 135.24 mg/g. Adsorption equilibrium could be quickly reached within 2 h. A kinetic study indicated that the adsorption of Cr(VI) conformed to the pseudo-second-order model (R² > 0.99). An intraparticle diffusion model was applied to describe the adsorption kinetics, and the results showed that there are other factors that affect the rate. Chemical regeneration for AC saturated with Cr(VI) was performed and HNO₃ displayed the best regeneration performance among the four chemical regeneration agents (HNO₃, H₂SO₄, NaOH, NaCl). The regeneration performance increased at first and then decreased with the rise of HNO₃ concentration, and regeneration reaction could reach equilibrium within 4 h in the first cycle. The FTIR spectra revealed that HNO₃ successfully introduced N-H bonds onto the AC surface in the regeneration process.

Carbon-Based Functional Materials Derived from Waste for Water Remediation and Energy Storage

Carbon-based functional materials hold the key for solving global challenges in the areas of water scarcity and the energy crisis. Although carbon nanotubes (CNTs) and graphene have shown promising results in various fields of application, their high preparation cost and low production yield still dramatically hinder their wide practical applications. Therefore, there is an urgent call for preparing carbon-based functional materials from low-cost, abundant, and sustainable sources. Recent innovative strategies have been developed to convert various waste materials into valuable carbon-based functional materials. These waste-derived carbon-based functional materials have shown great potential in many applications, especially as sorbents for water remediation and electrodes for energy storage. Here, the research progress in the preparation of waste-derived carbon-based functional materials is summarized, along with their applications in water remediation and energy storage; challenges and future research directions in this emerging research field are also discussed.

Synergistic effects of ion exchange and complexation processes in cysteine-modified clinoptilolite nanoparticles for removal of Cu(ii) from aqueous solutions in batch and continuous flow systems

In this work, clinoptilolite tuff was pre-treated and converted to microparticles (CMP) and nanoparticles (CNP) by a mechanical method.

CO2 Capture in the Sustainable Wheat-Derived Activated Microporous Carbon Compartments

Microporous carbon compartments (MCCs) were developed via controlled carbonization of wheat flour producing large cavities that allow CO2 gas molecules to access micropores and adsorb effectively. KOH activation of MCCs was conducted at 700 °C with varying mass ratios of KOH/C ranging from 1 to 5, and the effects of activation conditions on the prepared carbon materials in terms of the characteristics and behavior of CO2 adsorption were investigated. Textural properties, such as specific surface area and total pore volume, linearly increased with the KOH/C ratio, attributed to the development of pores and enlargement of pores within carbon. The highest CO2 adsorption capacities of 5.70 mol kg-1 at 0 °C and 3.48 mol kg-1 at 25 °C were obtained for MCC activated with a KOH/C ratio of 3 (MCC-K3). In addition, CO2 adsorption uptake was significantly dependent on the volume of narrow micropores with a pore size of less than 0.8 nm rather than the volume of larger pores or surface area. MCC-K3 also exhibited excellent cyclic stability, facile regeneration, and rapid adsorption kinetics. As compared to the pseudo-first-order model, the pseudo-second-order kinetic model described the experimental adsorption data methodically.

Adsorption–reduction of chromium(vi) from aqueous solution by phenol–formaldehyde resin microspheres

A novel adsorbent of phenol–formaldehyde resin (PF) microspheres was prepared at a low temperature, and had an excellent performance for the adsorption–reduction of Cr(vi).

Insights into mechanisms of hexavalent chromium removal from aqueous solution by using rice husk pretreated using hydrothermal carbonization technology

Hydrothermal carbonization technique enhanced the adsorption capacity of rice husk towards Cr(vi).

Optimization of production conditions for synthesis of chemically activated carbon produced from pine cone using response surface methodology for CO2 adsorption

A new insight to the production optimization of activated carbon from pine cone using RSM methodology for CO₂ adsorption.

One-step synthesis of magnetic 1,6-hexanediamine-functionalized reduced graphene oxide–zinc ferrite for fast adsorption of Cr(vi)

A one-step solvothermal method was developed to prepare nearly cubic ZnFe₂O₄ nanoparticles loaded on 1,6-hexanediamine-functionalized reduced graphene oxide (HDA–RGO–ZnFe₂O₄) for fast removal of Cr(vi).

Synthesis of poly(m-phenylenediamine)/iron oxide/acid oxidized multi-wall carbon nanotubes for removal of hexavalent chromium

Poly(m-phenylenediamine)-coated Fe₃O₄/o-MWCNTs nanoparticles (PmPD/Fe₃O₄/o-MWCNTs) were synthesized by one-step chemical oxidation polymerization.

Cr(VI) and azo dye removal using a hollow-fibre membrane system functionalized with a biogenic Pd-magnetite catalyst

This study investigates the application of a hybrid system combining hollow-fibre membrane technology with the reductive abilities of magnetic nanoparticles for the remediation of toxic Cr(VI) and the azo dye, Remazol Black B. Nano-scale biogenic magnetite (Fe3O4), formed by microbial reduction of the mineral ferrihydrite, has a high reductive capacity due to the presence of Fe(II) in the mineral structure. The magnetic nanoparticles (approximately 20 nm) can be arrayed with Pd0 nanoparticles (approximately 5 nm) making a catalytically active nanomaterial. Membrane units, with and without nanoparticles, were challenged with either Cr(VI) or azo dye and some were supplemented with sodium formate, as an electron donor for contaminant reduction promoted by the Pd. The combination of Pd-magnetite with formate resulted in the most effective remediation strategy for both contaminants and the lifetime of the membrane unit was also increased, with 55% (19 days) and 70% (23 days) removal of the azo dye and Cr(VI), respectively. Low flow rates of 0.1 ml/min resulted in improved efficiencies due to increased contact time with the membrane/nanoparticle unit, with 70-75% removal of each contaminant. Chemical analyses of the nanoparticles post-exposure to Cr(VI) in the membrane modules indicated Pd to be more oxidized when Cr removal was maximized, and that the Cr was partially reduced to Cr(III) at the surface of the magnetite. These results have demonstrated that hollow-fibre membrane units can be enhanced for the removal of soluble, redox sensitive contaminants by incorporation of a layer of palladized biogenic nanoparticulate magnetite.