Bohong Zheng

Effect of porous zinc–biochar nanocomposites on Cr(VI) adsorption from aqueous solution

A new synthesis method was developed to produce zinc–biochar nanocomposites from sugarcane bagasse. The modified biochar maintained 1.2 to 2.0 times higher removal efficiency than that of pristine biochar. FTIR, XPS, BET and SEM were used to analyse the physical and chemical properties of the composite adsorbent. Batch sorption experiments were carried out to investigate the adsorption behavior of Cr(VI) by zinc–biochar. Experimental data were better fitted by a pseudo-second-order kinetics equation and the Freundlich isotherm model. Thermodynamic analysis indicated that the adsorption process was spontaneous and endothermic. The maximum adsorption of the modified biochar was observed at pH 2.0 with the sorption capacity of 102.66 mg g−1. The adsorbed zinc–biochar could be effectively regenerated by 0.5 mol L−1 NaOH solution and the adsorption ability decreased from 84.16 to 59.75 mg g−1 in the sixth cycle. In conclusion, the porous zinc–biochar showed great potential advantages in the removal of Cr(VI) from wastewater.

Effective removal of Cr(VI) using β-cyclodextrin–chitosan modified biochars with adsorption/reduction bifuctional roles

In this work, beta-cyclodextrin–chitosan modified walnut shell biochars (β-CCWB) were synthesized as a low-cost adsorbent for the removal of heavy metal Cr(VI) from aqueous solutions. Batch sorption experiments were carried out to investigate the adsorption characteristic of β-CCWB. The experimental data fitted a pseudo-second order equation and Freundlich isotherm model, and the optimum adsorption of the modified biochar was observed at pH 2.0 with an adsorption capacity of 206 mg g−1. Thermodynamic analysis showed that the adsorption process was spontaneous and endothermic. The removal efficiency of Cr(VI) by β-CCWB (about 93%) was higher than that by the pristine biochar (about 27%). Characteristic analysis indicated that amino and carboxyl groups were the major functional groups for Cr(VI) sorption, and implied that the electrostatic attraction of Cr(VI) to the positively charged biochar surface, reduction of Cr(VI) to Cr(III) ions and the complexation between Cr(III) ions and β-CCWB functional groups were responsible for Cr(VI) removal mechanism in this research. Furthermore, the environmentally friendly and low-cost β-CCWB could be applied as a potential effective adsorbent to remediate Cr(VI) contamination from aqueous solution.

Biochar to improve soil fertility. A review

Soil mineral depletion is a major issue due mainly to soil erosion and nutrient leaching. The addition of biochar is a solution because biochar has been shown to improve soil fertility, to promote plant growth, to increase crop yield, and to reduce contaminations. We review here biochar potential to improve soil fertility. The main properties of biochar are the following: high surface area with many functional groups, high nutrient content, and slow-release fertilizer. We discuss the influence of feedstock, pyrolysis temperature, pH, application rates, and soil types. We review the mechanisms ruling the adsorption of nutrients by biochar.

Chitosan modification of magnetic biochar produced from Eichhornia crassipes for enhanced sorption of Cr(VI) from aqueous solution

In this research, chitosan modification of magnetic biochar (CMB) was successfully prepared for effective removal of Cr(VI). Moreover, this study highlighted that the conversion of Eichhornia crassipes into biochar was a promising method for improved management of this highly problematic invasive species. The sorption kinetics, isotherms, thermodynamics, the effects of pH, and background electrolyte on the sorption process were investigated. The results indicated that CMB adsorbed more Cr(VI) (120 mg g−1) than that of pristine biochar (30 mg g−1). The sorption data could be well illustrated by pseudo-second-order and Langmuir models. Furthermore, thermodynamic parameters revealed that the sorption reaction was an endothermic and spontaneous process. The adsorption of Cr(VI) was influenced by solution pH and the maximum sorption capacity was achieved at pH 2. The background electrolyte PO43− and SO42− restricted the Cr(VI) sorption. These results are significant for exploring and optimizing the removal of metal ions by the CMB composite.

Competitive removal of Cd(II) and Pb(II) by biochars produced from water hyacinths: performance and mechanism

Three biochars converted from water hyacinth biomass at 300, 450, and 600 °C were used to investigate the adsorption properties of Cd2+ and Pb2+. In addition, the competitive adsorption mechanisms between Cd2+ and Pb2+ were also conducted. Adsorption kinetics and isotherms indicated that the maximum adsorption capacity of Pb2+ was larger than that of Cd2+, and the adsorption process in the mixed solutions of two heavy metals (Cd2+ and Pb2+) was more favorable for Pb2+. Further investigation about the characterization of biochars demonstrated that cation exchange, surface complexation, cation–π interaction and precipitation were the main mechanisms responsible for the heavy metal removal. In this study, competitive adsorption may also be explained by these mechanisms. These results are useful for the application of biochars in selective adsorption and in practical wastewater treatment.

Effect of Cu(II) ions on the enhancement of tetracycline adsorption by Fe3O4@SiO2-Chitosan/graphene oxide nanocomposite.

Fe3O4@SiO2-Chitosan/GO (MSCG) nanocomposite was investigated by various techniques (SEM, TEM, XRD, VSM, FT-IR, XPS) for the removal of tetracycline (TC). Effects of pH, zeta potential and initial contaminant concentration were studied in detail. Four background cations (Na+, K+, Ca2+ and Mg2+) with a concentration of 0.01M showed little influence on the TC adsorption at the studied pH range while the divalent heavy metal cation Cu(II) could significantly enhance the adsorption. The results indicated that the highest adsorption capacity of TC were 183.47mmol/kg and 67.57mmol/kg on MSCG with and without Cu(II), respectively. According to mechanism investigation for the adsorption of TC by pH impact study and XPS analysis, besides electrostatic interaction and π-π interactions, the Cu(II) also acts as a bridge between TC and MSCG, which significantly improve the adsorption of TC. This study provided valuable guidance and effective method for the removal of TC from aquatic environments.

Adsorption behavior of Cr(VI) from aqueous solution onto magnetic graphene oxide functionalized with 1,2-diaminocyclohexanetetraacetic acid

A novel magnetic composite adsorbent was synthesized by grafting 1,2-diaminocyclohexanetetraacetic acid to magnetic graphene oxide (DCTA/E/MGO). The DCTA/E/MGO was employed for removing Cr(VI) from aqueous solution in this study. The composite was characterized by FESEM, TEM, BET, XRD, FT-IR and XPS. The adsorption behaviors of Cr(VI) by DCTA/E/MGO in aqueous solution were systematically investigated. Second order kinetic and Freundlich isotherm models validated the experimental data. The adsorption rate was influenced by both film diffusion and intraparticle diffusion. Thermodynamic parameters revealed that the adsorption reaction was an endothermic and spontaneous process. The novel adsorbent exhibited better Cr(VI) removal efficiency in solutions with low pH. The decontamination of Cr(VI) by DCTA/E/MGO was influenced by ionic strength. These results are important for estimating and optimizing the removal of metal ions by the DCTA/E/MGO composite.

Adsorption of hexavalent chromium by polyacrylonitrile (PAN)-based activated carbon fibers from aqueous solution

Polyacrylonitrile (PAN)-based activated carbon fibers (PAC400 and PAC600) were prepared by heating Zn(NO3)2 pretreated-PAN at 400 °C and 600 °C for the removal of Cr(VI) from aqueous solution. Formation of PAC400 and PAC600 was confirmed by FTIR and XPS. Field Emission Scanning Electron Microscopy (FESEM) imaging of PAC400 and PAC600 revealed the formation of nearly spherical agglomerated particles. The conditions for adsorption of Cr(VI) onto PAC400 and PAC600 had been optimized and kinetics and isotherm studies were performed. Although the adsorption took place in the range of pH (2–6), pH 3 was found to be most suitable. The adsorption data fitted well with the pseudo-second-order rate model and Langmuir isotherm model. PAC600 showed much greater ability in the adsorption of Cr(VI) than PAC400, and Qmax were calculated to be 187.79 mg g−1 and 136.87 mg g−1 based on the Langmuir model, respectively. Desorption experiments showed PAC600 and PAC400 can be regenerated and reused. The adsorption process for the removal of Cr(VI) was governed by the ionic interaction between protonated amine groups of PAC and HCrO4− ions.

Decontamination of methylene blue from aqueous solution by magnetic chitosan lignosulfonate grafted with graphene oxide: effects of environmental conditions and surfactant

In this study, magnetic chitosan lignosulfonate grafted with graphene oxide (MCLS/GO) as an innovative adsorbent was prepared successfully through a hydrothermal reaction. The adsorbent was also characterized using SEM, XRD, VSM, FTIR, XPS, and zeta-potential. The effects of pH, ionic strength, temperature and SDBS (sodium dodecylbenzene sulfonate) on the adsorption behavior of MB (methylene blue) by the MCLS/GO were investigated. The results indicate that MB removal is found to be more effective at a higher pH value and temperature. The adsorption process could be affected by ionic strength, particularly at a higher concentration. Isotherm and kinetics were well-fitted by a Langmuir isotherm model and pseudo-second-order model, respectively. In addition, the presence of SDBS had a positive effect on MB adsorption onto MCLS/GO. An intra-particle diffusion model indicates that both film diffusion and intra-particle diffusion were the rate-controlling processes. Thermodynamic analysis showed that the adsorption reaction was an endothermic and spontaneous process. The adsorption mechanism was proposed to be electrostatic attraction, π–π stacking interaction and hydrogen bonding via FTIR analysis. In conclusion, this study implies that MCLS/GO nanoparticles could be conveniently separated from a water body by an external magnet and utilized as an efficient adsorbent for environment purification.

Synthesis of graphene oxide decorated with core@double-shell nanoparticles and application for Cr(VI) removal

A novel graphene oxide composite, namely Fe3O4@SiO2@ chitosan/GO nanocomposite (MSCG) was synthesized for decontamination of Cr(VI) from aqueous solution. High-resolution transmission electron microscopy revealed a core@double-shell structure of the nanoparticles with iron oxide as the core, silica as the inner shell and chitosan as the outer shell. The characteristic results of Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM) and X-ray diffraction (XRD) showed that the Fe3O4@SiO2@chitosan particles were successfully assembled on the surface of the GO layers. The adsorption kinetics followed the pseudo-second-order model and the novel MSCG adsorbent exhibited better Cr(VI) removal efficiency in solutions at low pH. Thermodynamic parameters revealed that the sorption reaction was endothermic and spontaneous. Moreover, the adsorption capacity was about 90% of the initial saturation adsorption capacity after being used four times. By using a permanent magnet, the recycling process of both the MSCG adsorbents and the adsorbed Cr(VI) is more economically sustainable. These results suggest that MSCG is a potential and suitable candidate for the preconcentration and separation of Cr(VI) from wastewater and for the deep-purification of polluted water.