Biochar, derived from agricultural residuals, is extensively applied to remove detrimental heavy metals from wastewater, which has dual significance for the environment protection. Herein, the sorption behavior and interaction mechanism of Eu(III) on rice straw-derived biochar was investigated by batch and spectroscopic technologies. The solution pH significantly affects the percentage of the sorption, but has little effect on the contact time. Humic substances (HA/FA) significantly enhance Eu(III) sorption with solution pH<7.0, but inhibit the sorption with solution pH>7.0. The sorption mechanism involves co-precipitation or inner-sphere surface complexation. And the chemical sorption rate is restricted by intra-particle diffusion process. Besides, the Freundlich model simulates isotherms best and the maximum sorption amount is up to 40.717 mg/kg, which correlates with the stratified structure and abundant functional groups of biochar. The thermodynamic parameters suggest that the sorption of Eu(III) on biochar is a spontaneous and endothermic process. Therefore, these results are valuable to assess the potential application values of rice straw-derived biochar for the removal of Eu(III) in water systems.

Heavy metal chromium pollution seriously threatens the environmental safety of soil and water body. The Cr(VI) compound has strong migration ability, enrichment and strong oxidizing ability. These properties make Cr(VI) ions more dangerous and difficult to handle. Adsorption technology is a simple and effective method for treatment of heavy metal pollution. The two clay-biochars are made by mixing biochar derived from peanut shell and two kinds of clays (Kaolin and bentonite) under magnetic stirring conditions. A variety of characterizations suggest that clays uniformly deposit on the surface of biochar. Adsorption experiments indicate that the sorption of Cr(VI) ions from wastewater on Kaolin-biochar is significantly higher than that of bentonite-biochar. Adsorption kinetic of Cr (VI) on two clay-biochars follows satisfactorily the pseudo-second order model due to high correlation coefficient (R²>0.999). Adsorption isotherms of Cr(VI) on Biochar@Bentonite are fitted by Langmuir model, whereas the Freundlich model fits better the Cr(VI) sorption on Biochar@Kaolin. These findings are crucial for the potential application of clay-biochar composites for the treatment of the immobilization of heavy metals in environmental remediation.

Herein, the retention mechanisms and microstructure of Cd(II) on MoS₂ nanosheets were evaluated by batch experiments and EXAFS technology. The sorption of Cd(II) on MoS₂ was strongly affected by solution pH, contact time, and temperature, but not by the ionic strength. The solution pH could only promote the sorption capacity, but does not improve the sorption rates and change the sorption isotherms and thermodynamics in the pH range of 3.3-9.6. The pseudo-second-order model could fit the equilibrium data better and the intra-particle diffusion model showed three typical stages in the sorption process. The isotherms and thermodynamics analysis indicated that the heterogeneity sorption of Cd(II) onto MoS₂ was a spontaneous, endothermic, and irreversible process. The EXAFS spectra revealed the coexistence of two sorption types. The inner-sphere complexation was formed in the form of Cd-S bond at lower pH (3.56, 6.48), while the Cd(OH)₂ precipitation occurred in the form of Cd-O and Cd-Cd bonds at higher pH (9.57). These results provide new insights into the interaction mechanisms between metal ions and MoS₂ nanosheets.

In present work, a systematical and comprehensive understanding for the adsorption of Cd(II) on porous hexagonal boron nitride (p-BN) was studied. The chemical compositions, morphology and surface functional groups of p-BN before and after adsorption were characterized by SEM, HRTEM, BET, XRD, and FT-IR. The effects of pH, adsorbent dosage, contact time and temperature on Cd(II) adsorption were investigated. The maximum adsorption capacity for Cd(II) achieves 184 mg·g ^-1 at pH 7.0 and 313 K. The kinetic data fitted well with pseudo-second-order model and intra-particle diffusion model, indicating that the adsorption is mainly controlled by chemisorption, and the rate-limiting step is the molecular diffusion. The adsorption isotherms are in accordance with Freundlich and Langmuir model respectively, suggesting Cd(II) adsorbed on the heterogeneous surface through multilayer and monolayer adsorption. The thermodynamic parameters are calculated to confirm the spontaneous and endothermic process of Cd(II) sorption. Spectroscopic results from XPS imply that p-BN adsorbent had substantial functional groups and bonding sites, which is propitious to uptake Cd(II) from wastewater. These results revealed that p-BN is a promising candidate for Cd(II) scavenging.

Graphitic-like carbon nitride (g-C₃N₄), one of the most significant two-dimensional layered materials, has attracted worldwide attention in multidisciplinary areas such as photocatalysis, energy conversion and environmental pollution management. Its derivative compounds have also attracted multifarious attention owing to the intrinsic characters of their stable physicochemical properties, low cost and environmentally friendly features. This review focus on the design of high-performance g-C₃N₄-based nanomaterials and their potential for pollutant elimination in environmental pollution cleanup. Over the past few years, signi?cant advances have been achieved to synthesize g-C₃N₄ and g-C₃N₄-based nanomaterials, and their properties have been enhanced and characterized in detail. In this review, recent developments in the synthesis and modification of g-C₃N₄-based nanomaterials are summarized. The applications in heavy metal ions adsorption from wastewaters are gathered and their underlying reaction mechanisms are discussed. Finally, a summary and outlook are also briefly illustrated.