Adsorption characteristics and mechanisms of Pb2+ and Cd2+ by a new agricultural waste-Caragana korshinskii biomass derived biochar

In order to explore the comprehensive utilisation and recycling technology of Caragana korshinskii resources, a new agricultural biomass waste, 15 kinds of Caragana korshinskii biochar (CB) were prepared by controlling the pyrolysis temperature and time at the anaerobic environment. Moreover, we pay more attention to deriving the adsorption mechanisms and exploring the difference in adsorption characteristics of Pb²⁺ and Cd²⁺. The optimal preparation conditions and the batch adsorption experiments were evaluated, and the adsorption characteristics and mechanisms were discussed using 8 theoretical adsorption models and multiple characterisation methods. The results showed that the CB prepared at 650 °C for 3 h presented the best performance. The Langmuir and Freundlich models can well simulate the isotherm adsorption process of CB for Pb²⁺ and Cd²⁺, respectively. The adsorption kinetics of CB for Pb²⁺ and Cd²⁺ were best fitted by the pseudo-second-order model. The adsorption equilibrium for Pb²⁺ and Cd²⁺ was reached within 3 h, and their maximum adsorption capacity reached 220.94 mg g^-1 and 42.43 mg g^-1, respectively. In addition, the best addition amount was 3 g L^-1 and 2.2 g L^-1 for Pb²⁺ and Cd²⁺, respectively. The optimum pH range was 3-6 for Pb²⁺ and 6-7.5 for Cd²⁺. The adsorption mechanisms of CB for Pb²⁺ and Cd²⁺ were physicochemical composite adsorption processes, mainly including physical sorption on surface sites, intraparticle diffusion, electrostatic adsorption, ion/ligand exchange, cationic-π interactions, surface complexation and precipitation. Furthermore, the ash of CB also presented a positive effect on the adsorption of Pb²⁺. Compared with other cellulose- and lignin-based biomass materials, CB showed low cost and efficient performance without complicated modification conditions. Therefore, this study demonstrates that CB is a promising raw material in water pollution control to immobilise heavy metals.

Adsorption of P-Nitrophenol Onto Partially Reduced Graphene Oxide: An Experimental and Theoretical Study

This study investigated the adsorption process of p-nitrophenol ( p-NP) onto partially reduced graphene oxide (prGO) using both experiment and theoretical calculations. The maximum adsorption capacity of prGO at pH 6.0 and 293 K for p-NP was 29.94 mg g−1 which was significantly higher than previously reported using a metal-doped reduced graphene oxide composite. Systematic, comparative theoretical calculations were used to investigate the adsorption mechanism of p-NP onto graphene oxide, prGO and graphene nanosheet (GN). Calculations revealed three types of adsorption site and indicated that the adsorption force and sites were significantly affected by the quantity and type of oxygen-containing functional groups on the GN. The adsorption affinity was mainly derived from hydrogen bonds and π-π stacking which was further demonstrated by FTIR analysis. Due to its excellent adsorption performance, good recyclability and easy separation, prGO can be a promising adsorbent for the efficient elimination of p-NP from wastewater in the future.

Fe3O4 nanoparticle-coated mushroom source biomaterial for Cr(VI) polluted liquid treatment and mechanism research

Agrocybe cylindracea substrate-Fe3O4 (ACS-Fe3O4), a Fe3O4 nanoparticle-coated biomaterial derived from agriculture waste from mushroom cultivation, was developed to remove hexavalent chromium (Cr(VI)) from liquid. After modification, material surface became uneven with polyporous and crinkly structure which improved Cr-accommodation ability in a sound manner. Optimized by the Taguchi method, Cr(VI) removal percentage was up to 73.88 at 240 min, 40°C, pH 3, Cr(VI) concentration 200 mg l-1, dosage 12 g l-1, rpm 200. The efficient Cr(VI) removal was due to the combined effect of adsorption and redox. In addition, verification test using tannery wastewater, with removal percentage of Cr(VI) and total Cr reaching 98.35 and 95.6, provided further evidence for the efficiency and feasibility of ACS-Fe3O4. The effect of storage time of the material on Cr(VI) removal was small, which enhanced its value in practical application. Results indicated that metal removal was mainly influenced by solution concentration, adsorbent dosage and treatment time. The experimental data obtained were successfully fitted with the Langmuir isotherm model. Thermodynamic study indicated the endothermic nature of the process. The results confirmed that ACS-Fe3O4 as novel material derived from waste, with long-term stability, could be applied for heavy metal removal from wastewater and waste cycling.

Self-assembly modified-mushroom nanocomposite for rapid removal of hexavalent chromium from aqueous solution with bubbling fluidized bed

A self-assembled modified Pleurotus Cornucopiae material (SMPM) combined with improved Intermittent Bubbling Fluidized Bed (IBFB) was investigated to remove the hexavalent chromium ions in aqueous solution. After the modification, the powder-like raw material gradually self-assembled together to SMPM, which had crinkly porous structure, improved the Cr-accommodation ability in a sound manner. Optimized by Taguchi method, Cr(VI) removal efficiency was up to 75.91% and 48.01% for 100 mg/L and 500 mg/L initial concentration of Cr(VI), respectively. Results indicated that the metal removal was dependent on dosage of adsorbent, particle diameter and treatment time. The experimental data obtained from the biosorption process was successfully correlated with Freundlich isotherm model. Thermodynamic study indicated the endothermic nature of the process. The results confirmed that self-assembly modified Pleurotus Cornucopiae material could be applied for the removal of heavy metal from wastewater in continuous fluidized bed process.

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.

A novel graphene oxide coated biochar composite: synthesis, characterization and application for Cr(vi) removal

In the current work, a graphene oxide coated water hyacinth biochar composite (WHB-GO) was synthesized to remove Cr(vi) from aqueous solution.

Synthesis and adsorption application of amine shield-introduced-released porous chitosan hydrogel beads for removal of acid orange 7 from aqueous solutions

An effective and low-cost adsorbent named amine shield-introduced-released porous chitosan hydrogel beads (APCB) was synthesized and used for the removal of acid orange 7 from aqueous solutions.

Prospective application of Aspergillus species immobilized in sodium montmorillonite to remove toxic hexavalent chromium from wastewater

Aspergillus BRVR immobilized in sodium montmorillonite for the effective removal of Cr(vi) from waste water.