Mechanisms of metal sorption by biochars: Biochar characteristics and modifications

Preparation, modification and environmental application of biochar: A review

Biochar is a pyrogenous, organic material synthesized through pyrolysis of different biomass (plant or animal waste). The potential biochar applications include: (1) pollution remediation due to high CEC and specific surface area; (2) soil fertility improvement on the way of liming effect, enrichment in volatile matter and increase of pore volume, (3) carbon sequestration due to carbon and ash content, etc. Biochar properties are affected by several technological parameters, mainly pyrolysis temperature and feedstock kind, which differentiation can lead to products with a wide range of values of pH, specific surface area, pore volume, CEC, volatile matter, ash and carbon content. High pyrolysis temperature promotes the production of biochar with a strongly developed specific surface area, high porosity, pH as well as content of ash and carbon, but with low values of CEC and content of volatile matter. This is most likely due to significant degree of organic matter decomposition. Biochars produced from animal litter and solid waste feedstocks exhibit lower surface areas, carbon content, volatile matter and high CEC compared to biochars produced from crop residue and wood biomass, even at higher pyrolysis temperatures. The reason for this difference is considerable variation in lignin and cellulose content as well as in moisture content of biomass. The physicochemical properties of biochar determine application of this biomaterial as an additive to improve soil quality. This review succinctly presents the impact of pyrolysis temperature and the type of biomass on the physicochemical characteristics of biochar and its impact on soil fertility.

https://link.springer.com/content/pdf/10.1007/s11157-020-09523-3.pdf

Biochar physicochemical properties: pyrolysis temperature and feedstock kind effects

Surface functional groups of carbon-based adsorbents and their roles in the removal of heavy metals from aqueous solutions: A critical review.

Biochar-based nano-composites for the decontamination of wastewater: 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.

/pdf/biochar-to-improve-soil-fertility-a-review-okww45g9y9.pdf

Biochar to improve soil fertility. A review

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

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.

/pdf/effect-of-porous-zinc-biochar-nanocomposites-on-cr-vi-57ib3qeu77.pdf

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

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.

/pdf/effective-removal-of-cr-vi-using-b-cyclodextrin-chitosan-2alhuwckoy.pdf

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

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.

/pdf/chitosan-modification-of-magnetic-biochar-produced-from-3277fcvbt9.pdf

Bohong Zheng

Papers

Biochar to improve soil fertility. A review

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

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

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

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