Mechanism and industrial application feasibility analysis on microwave-assisted rapid synthesis of amino-carboxyl functionalized cellulose for enhanced heavy metal removal

Microwave-assisted one-pot preparation of magnetic cactus-derived hydrochar for efficient removal of lead(Ⅱ) and phenol from water: Performance and mechanism exploration

A novel magnetic hydrochar derived from cactus cladode (MW-MHC) was successfully synthesized through one-pot microwave-assisted process for efficiently removing lead(Pb)(Ⅱ) and phenol. From batch adsorption experiments, MW-MHC possessed the highest uptake amounts for Pb(Ⅱ) and phenol of 139.34 and 175.32 mg/g within 20 and 60 min, respectively. Moreover, the removal of Pb(Ⅱ) and phenol by MW-MHC remained essentially stable under the interference of different co-existing cations, presenting the excellent adaptability of MW-MHC. After three cycles of regeneration experiments, MW-MHC still had preferable adsorption performance and could be easily recycled, indicating its excellent reusability. Significantly, the uptake mechanisms of Pb(Ⅱ) on MW-MHC were regarded as chemical complexation, pore filling, precipitation, and electrostatic attraction. Meanwhile, the phenol uptake might be dominated by π-π interaction and hydrogen bonding. The above consequences revealed that MW-MHC with high removal performance was a promising adsorbent for remediating wastewater containing heavy metals and organics.

Do tillage systems affect the cadmium threshold in farmland soil for environmental quality standard setting?

Tillage systems may change the cadmium (Cd) threshold of farmland soil. However, there have been few studies on this topic. Therefore, this study aimed to explore the influence of tillage systems on Cd threshold. The study conducted 2-year field experiments under different tillage systems (early rice-fallow, early rice-late rice and early rice-vegetable) at three typical Cd-polluted sites in China. The species sensitivity distribution (SSD) method was used to construct the SSD curves for the calculation of the Cd threshold by analyzing the experimental data. The sensitivity analysis results based on the SSD curves revealed that the sensitivities to Cd in rice varieties under the same tillage system were substantially different but almost the same under different tillage systems. These results can help select rice varieties with low Cd sensitivity for crop safety. Different tillage systems at the same site varied in their influence on Cd threshold values. Cd threshold values under early rice-late rice (e.g., 0.27, 0.28 mg/kg in Xiangtan City) and early rice-vegetable (e.g., 0.26, 0.31 mg/kg in Xiangtan City) tillage systems were roughly lower than that under the early rice-fallow tillage system (e.g., 0.33, 0.35 mg/kg in Xiangtan City). Notably, the influence of tillage systems resulted in Cd threshold values being generally lower than the Cd risk screening values of the current Chinese soil environmental quality standard. Analysis of the influence of different tillage systems on the Cd threshold is beneficial for the optimization of farmland soil environmental quality standards.

Bibliometric Analysis of the Influencing Factors, Derivation, and Application of Heavy Metal Thresholds in Soil

The study of threshold levels of heavy metals in soil is essential for the assessment and management of soil environmental quality. This study reviewed the influencing factors, the derivation, and application aspects of heavy metals' threshold values comprehensively by a combination of bibliometric analysis and scientific knowledge mapping. A total of 1106 related studies were comprehensively extracted from the Web of Science database during the period from 2001 to 2020. The results showed that the publication output has been growing strongly. An analysis on the subject, journal, country, and institution was carried out to demonstrate the development and evolution of this research branch during the two decades. According to high-frequency keywords analysis, external factors (e.g., soil physicochemical properties) and internal factors (e.g., crop genotype) can affect heavy metal threshold values in the soil-crop system. The current methods mainly include the Point model (e.g., evaluation factor method), the Probability model (e.g., species sensitivity distribution method), and the Empirical model (e.g., ecological environment effect method). A threshold study can be applicable to the risk assessment for soil heavy metal contamination in order to determinate the soil pollution degree and its spatial and temporal distribution characteristics. Moreover, challenges and prospects of the study of heavy metal threshold values are proposed, indicating that research should focus on the relationships between human health risks and the established threshold values of heavy metals in the soil, long-term field trials and bioavailability of heavy metals for the derivation of the thresholds, and the establishment of more scientific and rational soil environmental benchmarks.

The effective removal of Pb2+ by activated carbon fibers modified by l-cysteine: exploration of kinetics, thermodynamics and mechanism

Herein, we developed a low-cost fabrication route to prepare chemically grafted activated carbon fibers, which effectively removed Pb²⁺ from solution. Multiple characteristic results indicated that l-cyst-ACF had abundant nitrogen-containing and sulfur-containing functional groups. Based on the XPS and EDS analyses, the capture of Pb²⁺ was attributed to the abundant adsorption sites on the fiber surface. According to the analysis of the pseudo-second-order kinetic model and the Langmuir isotherm model, the adsorption process could be interpreted as monolayer adsorption and chemisorption, and the equilibrium adsorption capacity was determined to be 136.80 mg g⁻¹ by fitting the pseudo-second-order kinetic model. The maximum adsorption capacity of l-cyst-ACF for Pb²⁺ was calculated to be 179.53 mg g⁻¹ using the Langmuir model. In addition, the adsorption reaction was endothermic and spontaneous, as evidenced by the thermodynamic parameters. The outcomes of this study provide a low-cost and feasible strategy for the remediation of Pb²⁺ pollution in the environment.

A low-cost fabrication route has been developed to prepare a chemically grafted activated carbon fiber, which effectively removed Pb²⁺ from solution. Multiple characterisation results indicated that l-cyst-ACF had abundant N-containing and S-containing functional groups.

Advanced nanocellulose-based gas barrier materials: Present status and prospects

Nanocellulose based gas barrier materials have become an increasingly important subject, since it is a widespread environmentally friendly natural polymer. Previous studies have shown that super-high gas barrier can be achieved with pure and hierarchical nanocellulose films fabricated through simple suspension or layer-by-layer technique either by itself or incorporating with other polymers or nanoparticles. Improved gas barrier properties were observed for nanocellulose-reinforced composites, where nanocellulose partially impermeable nanoparticles decreased gas permeability effectively. However, for nanocellulose-based materials, the higher gas barrier performance is jeopardized by water absorption and shape deformation under high humidity conditions which is a challenge for maintaining properties in material applications. Thus, numerous investigations have been done to solve the problem of water absorption in nanocellulose-based materials. In this literature review, gas barrier properties of pure, layer-by-layer and composite nanocellulose films are investigated. The possible theoretical gas barrier mechanisms are described, and the prospects for nanocellulose-based materials are discussed.

Cholesteric Molecular Tweezer Artificial Receptor for Rapid and Highly Selective Detection of Ag+ in Food Samples

Chiral cholesteric molecular tweezer 7a was synthesized, and its recognition properties for Ag⁺, Al³⁺, Ca²⁺ etc., were investigated by UV and fluorescence spectra. The results showed that in ethanol/Tris (1/1, v/v, pH 7.0) buffer solution, the host molecular tweezer 7a had a specific recognition ability for Ag⁺, the detection limit was up to 1 × 10⁻⁶ mol/L, and other metal ions had little effect on Ag⁺ recognition. At the same time, the naked-eye detection of Ag⁺ was realized by the light red color of the complex solution. Furthermore, the mechanism of recognition of Ag⁺ by molecular tweezer 7a was studied by a nuclear magnetic titration test and computer molecular simulation, and a rapid detection method of Ag⁺ using host molecular tweezer 7a was established. Through the determination of Ag⁺ in milk powder, quinoa and other food samples, it was proved that this novel method had a good application prospect for the detection of Ag⁺ in food.

Magnetic field-influenced nanofiltration membrane blended by CS-EDTA-mGO as multi-functionality green modifier to enhance nanofiltration performance, efficient removal of Na2SO4/Pb2+/RR195 and cyclic wastewater treatment

Magnetic field-influenced nanofiltration membrane by blending of magnetic multi-functionality green modifier (CS-EDTA-mGO) was fabricated via phase inversion processes. Migration of superparamagnetic nanofiller particles into top surface layer of M6 NF-membrane by incorporating external magnetic-filed during casting phase improved the hydrophilicity, as well as formation of large pores diameters (1.57 nm) which offer a flux enhancement (84.2 kg/m²h), excellent fouling resistance (R_r of 26.4%, R_t of 39.4% and R_ir of 25.0%) and highest flux recovery ratio (75.9%). The order of salt rejection for all modified NF-membranes was Na₂SO₄ > MgSO₄ > NaCl and the efficiency of the membranes to reject salts follows the order of M6 > M4 > M0. The performance of M6 as magnetic field-influenced membrane in rejection of RR195 and MB was 21% and 42% higher than unblended membrane (M0), respectively. The highest removal efficiency of Pb²⁺ and Cd²⁺ observed for M6 (98.2% and 93.6%, respectively). M6 was more efficient in concurrent removing pollutants from mixed-solute feed. In this case, the existing of Na₂SO₄ enhanced the retention of RR195 from 97.2% to 99.3%. Long-term operation tests demonstrated the excellent stability of M6 for 18 h filtration with a limited reduction in rejection and water flux of single salt solution. M6 membrane has found potential application in cyclic textile wastewater treatment which the water flux was found to be constant over 3-repeated filtration cycles.