Mechanochemical modification of biochar-attapulgite nanocomposites for cadmium removal: Performance and mechanisms

Pristine and modified biochar applications as multifunctional component towards sustainable future: Recent advances and new insights

Employing biomass for environmental conservation is regarded as a successful and environmentally friendly technique since they are cost-effective, renewable, and abundant. Biochar (BC), a thermochemically converted biomass, has a considerably lower production cost than the other conventional activated carbons. This material's distinctive properties, including a high carbon content, good electrical conductivity (EC), high stability, and a large surface area, can be utilized in various research fields. BC is feasible as a renewable source for potential applications that may achieve a comprehensive economic niche. Despite being an inexpensive and environmentally sustainable product, research has indicated that pristine BC possesses restricted properties that prevent it from fulfilling the intended remediation objectives. Consequently, modifications must be made to BC to strengthen its physicochemical properties and, thereby, its efficacy in decontaminating the environment. Modified BC, an enhanced iteration of BC, has garnered considerable interest within academia. Many modification techniques have been suggested to augment BC's functionality, including its adsorption and immobilization reliability. Modified BC is overviewed in its production, functionality, applications, and regeneration. This work provides a holistic review of the recent advances in synthesizing modified BC through physical, chemical, or biological methods to achieve enhanced performance in a specific application, which has generated considerable research interest. Surface chemistry modifications require the initiation of surface functional groups, which can be accomplished through various techniques. Therefore, the fundamental objective of these modification techniques is to improve the efficacy of BC contaminant removal, typically through adjustments in its physical or chemical characteristics, including surface area or functionality. In addition, this article summarized and discussed the applications and related mechanisms of modified BC in environmental decontamination, focusing on applying it as an ideal adsorbent, soil amendment, catalyst, electrochemical device, and anaerobic digestion (AD) promoter. Current research trends, future directions, and academic demands were available in this study.

Mitigation of Cd(II) contamination in aqueous solution and soil by multifunctional hydroxyapatite/sludge biochar composite

Biochar with well-developed pore structure is an ideal carrier for easily agglomerated hydroxyapatite (HAP). Hence, a novel multifunctional hydroxyapatite/sludge biochar composite (HAP@BC) was synthesized by chemical precipitation method and used for mitigating Cd(II) contamination form aqueous solution/soil. Compared to sludge biochar (BC), HAP@BC exhibited rougher and more porous surface. Meanwhile, the HAP was dispersed on the sludge biochar surface, which reduced the agglomeration of HAP. The adsorption performance of HAP@BC on Cd(II) was better than that of BC under the influence of different single-factor batch adsorption experiments. Moreover, the Cd(II) adsorption behavior by BC and HAP@BC was uniform monolayer adsorption, and this reaction process was endothermic and spontaneous. The Cd(II) maximum adsorption capacities of BC and HAP@BC were 79.96 and 190.72 mg/g at 298 K, respectively. Moreover, the Cd(II) adsorption mechanism on BC and HAP@BC included complexation, ion exchange, dissolution-precipitation and Cd(II)-π interaction. According to the semi-quantitative analysis, ion exchange was the main mechanism for Cd(II) removal by HAP@BC. Notably, HAP played a role in the Cd(II) removal by dissolution-precipitation and ion exchange. This result suggested that there was a synergistic effect between HAP and sludge biochar for the Cd(II) removal. HAP@BC reduced the leaching toxicity of Cd(II) in soil better than BC, indicating that the HAP@BC was able to mitigate Cd(II) contamination in soil more effectively. This work demonstrated that sludge biochar was an ideal carrier for dispersed HAP and provided an effective HAP/biochar composite for the mitigation of Cd(II) contamination in aqueous solution/soil.

Effect of humic acid-modified attapulgite on polycyclic aromatic hydrocarbon adsorption and release from paddy soil into the overlying water in a rice-crab coculture paddy ecosystem and the underlying process

Phenanthrene (Phe), a typical polycyclic aromatic hydrocarbon (PAH) pollutant, poses an enormous safety risk to rice-crab coculture (RC) paddy ecosystems. In this study, humic acid-modified purified attapulgite (HA-ATP) with a composite structure was successfully fabricated to adsorb PAHs released from paddy soil to overlying water in RC paddy ecosystems in Northeast China. The maximum crab bioturbation intensities for dissolved Phe and particulate Phe were 64.83nullng/L·(cm²·d) and 214.29nullng/L·(cm²·d), respectively. The highest concentration of dissolved Phe released from paddy soil to overlying water due to crab bioturbation reached 80.89nullng/L, while the corresponding concentration of particulate Phe reached 267.36nullng/L. The dissolved organic carbon (DOC) and total suspended solid (TSS) concentrations in overlying water increased correspondingly and were strongly correlated with dissolved Phe and particulate Phe concentrations, respectively (P < 0.05). When 6% HA-ATP was added to the surface layer of paddy soil, the efficiency of the adsorption of Phe release was 24.00%-36.38% for particulate Phe and 89.99%-91.91% for dissolved Phe. Because HA-ATP has a large adsorption pore size (11.33 nm) and surface area (82.41nullm²/g) as well as many HA functional groups, it provided multiple hydrophobic adsorption sites for dissolved Phe, which was conducive to competitive adsorption with DOC in the overlying water. In contrast to that adsorbed by DOC, the average proportion of dissolved Phe adsorbed by HA-ATP reached 90.55%, which reduced the dissolved Phe concentration in the overlying water. Furthermore, even though the particulate Phe was resuspended by crab bioturbation, HA-ATP immobilized particulate Phe due to its capacity to inhibit desorption, which achieved the goal of reducing the Phe concentration in the overlying water. This result was confirmed by research on the adsorption-desorption characteristics of HA-ATP. This research provides an environmentally friendly in situ remediation method for reducing agricultural environmental risks and improving rice crop quality.

Mechanochemical modified nitrogen-rich biochar derived from shrimp shell: Dominant mechanism in pyridinic-N for aquatic methylene blue removal

N-doping for the preparation of functional carbon materials is a trending research topic. In this study, N-rich biochar (BC) was prepared by calcining naturally N rich shrimp shells under oxygen-limiting environment, and the calcining temperatures were controlled. BC were activated with 5% hydrochloric acid solutions and then post-modified with ball-milling to obtain a series of novel adsorbents (MBCs). All samples were characterized by SEM, BET, FT-IR, XRD, XPS, TG, and element analysis. Surface area, pore volume, and other surface functional groups were significantly improved after acidizing and ball-milling. The adsorption capacities for MB were MBC350 > MBC500 > MBC650 >BC350 > BC650 > BC500, and the equilibrium adsorption capacities were 575.01 mg/g, 506.52 mg/g, 424.59 mg/g, 113.31 mg/g, 93.53 mg/g and 86.25 mg/g, respectively. The excellent adsorption performance of MBCs for MB was ascribed to Lewis acid-base interaction, π-π interaction, electrostatic interaction and van der Waals, and the quinone group and pyridinic-N on the surface of the MBCs are identified as the major active sites. Taken together, ball-milled shrimp shell biochar is a promising material for cation dye adsorption.

Removal of Cd(2+) from wastewater to form a three-dimensional fiber network using Si-Mg doped industrial lignin-based carbon materials

In this study, SiMg doped industrial lignin-based carbon materials (SLCs) were prepared by water bath silicification and MgCl₂ activation to remove Cd²⁺ from aqueous solutions. What's more, the doping of SiMg jointly promoted the excellent physicochemical properties of the material, e.g., high specific surface area, good pore volume, and numerous oxygen-containing groups. The Cd²⁺ batch adsorption experiments proved that SLCs have good Cd²⁺ removal capacity within pH 3-7, and the adsorption model demonstrated the adsorption process as a physicochemically complex process. The maximum adsorption of Cd²⁺ in the SLC was 665.35 mg/g, and the contributing factors to the removal of Cd²⁺ were as follows: ion exchange (59.36 %) > Cd²⁺ precipitation (24.93 %) > oxygen-containing functional group complexation (14.79 %) > Cd²⁺-π interactions (0.92 %). In addition, the complexation of SiO, MgO, and Cd precipitates allowed the formation of a three-dimensional fiber mesh structure. The application of SLCs has the potential to eliminate Cd²⁺ pollution in water bodies, and its preparation is simple and environmentally friendly. Finally, this study provides a theoretical basis for an in-depth understanding of the mechanism of heavy metal adsorption by inorganic nonmetals in combination with metal oxides.

Enhanced Adsorption of Sulfonamides by Attapulgite-Doped Biochar Prepared with Calcination

The extensive use of sulfonamides seriously threatens the safety and stability of the ecological environment. Developing green inexpensive and effective adsorbents is critically needed for the elimination of sulfonamides from wastewater. The non-modified biochar exhibited limited adsorption capacity for sulfonamides. In this study, the attapulgite-doped biochar adsorbent (ATP/BC) was produced from attapulgite and rice straw by calcination. Compared with non-modified biochar, the specific surface area of ATP/BC increased by 73.53−131.26%, and the average pore width of ATP/BC decreased 1.77−3.60 nm. The removal rates of sulfadiazine and sulfamethazine by ATP/BC were 98.63% and 98.24%, respectively, at the mass ratio of ATP to rice straw = 1:10, time = 4 h, dosage = 2 g∙L−1, pH = 5, initial concentration = 1 mg∙L−1, and temperature = 20 °C. A pseudo-second-order kinetic model (R2 = 0.99) and the Freundlich isothermal model (R2 = 0.99) well described the process of sulfonamide adsorption on ATP/BC. Thermodynamic calculations showed that the adsorption behavior of sulfonamides on the ATP/BC was an endothermic (ΔH > 0), random (ΔS > 0), spontaneous reaction (ΔG < 0) that was dominated by chemisorption (−20 kJ∙mol−1 > ΔG). The potential adsorption mechanisms include electrostatic interaction, hydrogen bonding, π−π interaction, and Lewis acid−base interactions. This study provides an optional material to treat sulfonamides in wastewater and groundwater.