Surface characterization of maize-straw-derived biochar and their sorption mechanism for Pb2+ and methylene blue

Effect of a sodium carboxymethyl cellulose composite hydrogel on tobacco growth and development under drought stress

In order to promote the growth and development of tobacco and reduce the adverse effects of drought on tobacco, acrylamide/sodium carboxymethyl cellulose/modified biochar hydrogel (AM/CMC/MB) was prepared by crosslinking polymerization reaction. The structural characteristics of the hydrogel were comprehensively analysed using Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Additionally, the water absorption capacity of the hydrogel was quantitatively evaluated. Furthermore, this study investigated the efficacy of AM/CMC/MB hydrogel in promoting the growth and development of potted tobacco seedlings under drought stress conditions. The results showed that the equilibrium solubility of AM/CMC/MB hydrogel was increased by 74.83 % and the diffusion process of water molecules followed the non-Fickian diffusion law compared with commercially available water retention agents. The openness of stomata of tobacco seedlings and the SPAD values were improved. The MDA (Malondialdehyde) content of tobacco seedlings was reduced by 47.50 %, CAT (Antioxidant enzymes catalase) and POD (Peroxidase) activities were increased by 198.15 % and 198.23 %, respectively. The total amount of metabolites detected after drought in tobacco seedlings supplemented with hydrogel AM/CMC/MB was increased by 50.33 % as compared to the control. This study provides a basis for the use of AM/CMC/MB as a water retention agent for tobacco growth and development.

Amino-modified upcycled biochar achieves selective chromium removal in complex aqueous matrices

Chromium pollution of groundwater sources is a growing global issue, which correlates with various anthropogenic activities. Remediation of both the Cr(VI) and Cr(III), via adsorption technologies, has been championed in recent years due to ease of use, minimal energy requirements, and the potential to serve as a highly sustainable remediation technology. In the present study, a biochar sorbent sourced from pineapple skins, allowed for the upcycling of agricultural waste into water purification technology. The biochar material was chemically modified, through a green amination method, to produce an efficient and selective adsorbent for the removal of both Cr(VI) and Cr(III) from complex aqueous matrices. From FTIR analysis it was evident that the chemical modification introduced new C-N and N-H bonds observed in the modified biochar along with a depletion of N-O and C-H bonds found in the pristine biochar. The amino modified biochar was found to spontaneously adsorb both forms of chromium at room temperature, with binding capacities of 46.5 mg/g of Cr(VI) and 27.1 mg/g of Cr(III). Interference studies, conducted in complex matrices, showed no change in adsorption capacity for Cr(VI) in matrices containing up to 3,000× the concentration of interfering ions. Finally, Cr(III) removal was synergized to 100% adsorption at interfering ions concentrations up to 330× of the analyte, which were suppressed at higher interference concentrations. Considering such performance, the amino modified biochar achieved selective removal for both forms of chromium, showing great potential for utilization in complex chromium pollution sources.

Remarkable synergy between sawdust biochar and attapulgite/diatomite after co-ball milling to adsorb methylene blue

Biochar has been recognized as a promising sustainable adsorbent for removing pollutants from wastewater. In this study, two natural minerals, attapulgite (ATP) and diatomite (DE) were co-ball milled with sawdust biochar (pyrolyzed at 600 °C for 2 h) at ratios of 10-40% (w/w) and examined the ability of methylene blue (MB) to be removed from aqueous solutions by them. All the mineral-biochar composites sorbed more MB than both ball milled biochar (MBC) and ball milled mineral alone, indicating there was a positive synergy in co-ball milling biochar with these minerals. The 10% (w/w) composites of ATP:BC (MABC10%) and DE:BC (MDBC10%) had the greatest MB maximum adsorption capacities (modeled by Langmuir isotherm modeling) and were 2.7 and 2.3 times that of MBC, respectively. The adsorption capacities of MABC10% and MDBA10% were 183.0 mg g^-1 and 155.0 mg g^-1 at adsorption equilibrium, respectively. These improvements can be owing to the greater content of oxygen-containing functional groups and higher cation exchange capacity of the MABC10% and MDBC10% composites. In addition, the characterization results also reveal that pore filling, π-π stacking interactions, hydrogen bonding of hydrophilic functional groups, and electrostatic adsorption of oxygen-containing functional groups also contribute prominently to the adsorption of MB. This, along with the greater MB adsorption at higher pH and ionic strengths, suggests the roles in MB adsorption was an electrostatic interaction and an ion exchange mechanism. These results demonstrate that mineral-biochar composites prepared by co-ball milling treatment were promising sorbents of ionic contaminants for environmental applications.

Chitosan-modified biochar: Preparation, modifications, mechanisms and applications

The chitosan-modified biochar composite, as a carbohydrate polymer, has received increasing attention and becomes a research hotspot. It is a promising impurity adsorption material, which has potential application value in the agricultural environment fields such as soil improvement and sewage purification. The composite can combine the advantages of biochar with chitosan, and the resulting composite usually exhibits a great improvement in its surface functional groups, adsorption sites, stability, and adsorption properties. In addition, compared to other adsorbents, the composite truly achieves the concept of "waste control by waste". In this paper, the preparation method, composite classification, adsorption mechanism, and models of biochar modified by chitosan are introduced, meanwhile, we also review and summarize their effects on the decontamination of wastewater and soil. In addition to common heavy metal ions, we also review the adsorption and removal of some other organic/inorganic pollutants, including (1) drug residues; (2) dyes; (3) phosphates; (4) radionuclides; (5) perfluorochemicals, etc. Moreover, challenges and prospects for the composite are presented and further studies are called for the chitosan-biochar composite. We believe that the composite will lead to further achievements in the field of environmental remediation.

Versatile Strategy for the Preparation of Woody Biochar with Oxygen-Rich Groups and Enhanced Porosity for Highly Efficient Cr(VI) Removal

Biochar is widely used to remove hexavalent chromium [Cr(VI)] from wastewater through adsorption, which is recognized as a facile, cost-efficient, and high-selectivity approach. In this study, a versatile strategy that combines delignification with subsequent carbonization and KOH activation is proposed to prepare a novel woody biochar from waste poplar sawdust. By virtue of the unique multilayered and honeycomb porous structure induced by delignification and activation processes, the resultant activated carbonized delignified wood (ACDW) exhibits a high specific surface area of 970.52 m2 g-1 with increasing meso- and micropores and abundant oxygen-containing functional groups. As a benign adsorbent for the uptake of Cr(VI) in wastewater, ACDW delivers a remarkable adsorption capacity of 294.86 mg g-1 in maximum, which is significantly superior to that of unmodified counterparts and other reported biochars. Besides, the adsorption behaviors fit better with the Langmuir isotherm, the pseudo-second-order kinetic model, and the adsorption diffusion model in batch experiments. Based on the results, we put forward the conceivable adsorption mechanism that the synergistic contributions of the capillary force, electrostatic attraction, chemical complexation, and reduction action facilitate the Cr(VI) capture by ACDW.

Preparation of Porous Biochar from Soapberry Pericarp at Severe Carbonization Conditions

The residue remaining after the water extraction of soapberry pericarp from a biotechnology plant was used to produce a series of biochar products at pyrolytic temperatures (i.e., 400, 500, 600, 700 and 800 °C) for 20 min plant was used to produce a series of biochar products. The effects of the carbonization temperature on the pore and chemical properties were investigated by using N2 adsorption–desorption isotherms, energy dispersive X-ray spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FTIR). The pore properties of the resulting biochar products significantly increased as the carbonization temperature increased from 700 to 800 °C. The biochar prepared at 800 °C yielded the maximal BET surface area of 277 m2/g and total pore volume of 0.153 cm3/g, showing that the percentages of micropores and mesopores were 78% and 22%, respectively. Based on the findings of the EDS and the FTIR, the resulting biochar product may be more hydrophilic because it is rich in functional oxygen-containing groups on the surface. These results suggest that soapberry pericarp can be reused as an excellent precursor for preparing micro-mesoporous biochar products in severe carbonization conditions.

Analysis of the Cd(II) Adsorption Performance and Mechanisms by Soybean Root Biochar: Effect of Pyrolysis Temperatures

As one of the most harmful environmental pollutants, cadmium (Cd) has arisen much interest, and many researches have been carried out to study the adsorption of heavy metals by biochar, but the mechanisms were poorly explored and the roles components in biochar played are still indistinct. In this study, we evaluated the adsorption capacities and mechanisms of soybean root biochar pyrolyzed at four different temperatures. The results indicate the biochar properties are significantly determined by pyrolysis temperature, which affects the removal mechanisms of Cd(II) consequently. Microstructure characteristics and mechanism analysis further suggest that Cd(II)-π interactions and sulfur-containing functional groups are the main mechanisms of Cd(II) adsorption. This work shows a new perspective to explain the adsorption mechanisms onto biochar adsorbents and has a benefit for the exploitation of economical and effective adsorbents for Cd(II) removal based on biochars.

Correction: Surface characterization of maize-straw-derived biochar and their sorption mechanism for Pb2+ and methylene blue

[This corrects the article DOI: 10.1371/journal.pone.0238105.].