Efficient adsorption of hexavalent chromium in water by torrefaction biochar from lignin-rich kiwifruit branches: The combination of experiment, 2D-COS and DFT calculation.

A biochar (KBC) enriched with O functional groups was prepared by torrefaction using lignin-rich kiwifruit branches (KBM) as a raw material, which was characterized, and then KBC was used to adsorb hexavalent chromium (Cr6+) from water. The results showed that KBC contained more functional groups compared to KBM. The maximum adsorption of Cr6+ by KBC could reach 143.64 mg·g-1 and also had better adsorption performance than other adsorbents reported in some other reports. Cr6+ absorption by KBC was mainly a mechanism of electrostatic interaction and adsorption-reduction coupling. FTIR and XPS revealed that -OH, -COOH, CO and CC on KBC participated in Cr6+ adsorption and new groups (C=O) were generated during the process of adsorption, which implied that a redox reaction occurred. 2D-COS and DFT calculations showed that the order of functional groups on KBC interacting with Cr6+ was -OCH3 > -COOH > -OH > phenolic hydroxyl, and the binding tightness of the different functional groups to Cr6+ was -OCH3 (the shortest displacement of both groups after the adsorption) > -COOH > -OH > phenolic hydroxyl. KBC has good regeneration performance, and it is a good adsorbent for Cr6+.

Performance and Mechanism of Functionalized Water Hyacinth Biochar for Adsorption and Removal of Benzotriazole and Lead in Water.

In this paper, water hyacinth is used to prepare biochar (WBC). A biochar-aluminum-zinc-layered double hydroxide composite functional material (WL) is synthesized via a simple co-precipitation method which is used to adsorb and remove benzotriazole (BTA) and lead (Pb2+) in an aqueous solution. In particular, this research paper uses various characterization methods to analyze WL and to explore the adsorption performance and adsorption mechanism of WL on BTA and Pb2+ in an aqueous solution through batch adsorption experiments combined with model fitting and spectroscopy techniques. The results indicate that the surface of WL contains a thick sheet-like structure with many wrinkles which would provide many adsorption sites for pollutants. At room temperature (25 °C), the maximum adsorption capacities of WL on BTA and Pb2+ are 248.44 mg·g-1 and 227.13 mg·g-1, respectively. In a binary system, during the process of using WL to adsorb BTA and Pb2+, compared with that in the absorption on Pb2+, WL shows a stronger affinity in the adsorption on BTA, and BTA would thus be preferred in the absorption process. The adsorption process of WL on BTA and Pb2+ is spontaneous and is endothermic monolayer chemisorption. In addition, the adsorption of WL on BTA and Pb2+ involves many mechanisms, but the main adsorption mechanisms are different. Among them, hydrogen bonding dominates the adsorption on BTA, while functional groups (C-O and C=O) complexation dominates the adsorption on Pb2+. When WL adsorbs BTA and Pb2+, the coexistence of cations (K+, Na+, and Ca2+) has a strong anti-interference ability, and WL can use a lower concentration of fulvic acid (FA) (<20 mg·L-1) to improve its adsorption performance. Last but not least, WL has a stable regenerative performance in a one-component system and a binary system, which indicates that WL has excellent potential for the remediation of BTA and Pb2+ in water.

Adsorption of chitosan combined with nicotinamide-modified eupatorium adenophorum biochar to Sb3+: Application of DFT calculation.

The pollution and harm of Sb3+ to aquatic systems is a global problem, so Sb3+ removal from the water environment to make sure environment safety and human beings wellbeing is of urgency. This study explored the effect of chitosan combined with nicotinamide-modified eupatorium adenophorum biochar (CEBC) on adsorbing Sb3+ through batch adsorption experiments. The experiments indicated CEBC's maximum adsorption capacity to Sb3+ is 170.15 mg·g-1. Meanwhile, the capacity of the original biochar (EBC) is only 9.97 mg·g-1. Compared with EBC, CEBC contains more functional groups, such as CO, -OH and -NH2. In addition, the pseudo-second-order kinetic model and the Langmuir model are fit to describe the kinetics and isotherms of adsorption of CEBC to Sb3+, which suggests that the adsorption of CEBC to Sb3+ is dominated by monolayer chemisorption. Density functional theory (DFT) calculations confirmed that the chelation between -NH2 and Sb3+ is of significance in the adsorption process of CEBC. DFT calculations also found that the newly added -OH and CO in EBC have a synergistic enhancement effect on the absorption of Sb3+. The mechanism of CEBC absorbing Sb3+ includes electrostatic interactions, pore filling, Л-Л interactions, hydrogen bonding, functional group complexation, chelation, and oxidation. CEBC has an excellent anti-interference ability for inorganic anions (NO3-, SO42- and Cl-) and can also use the coexisting HA to improve its adsorption performance. In addition, CEBC has better mitigation of Sb3+ on the performance of Sb3+ about its secondary release and good reproducibility, which indicates that CEBC is a viable Sb3+ adsorbent.

Effects of irrigation on the fate of microplastics in typical agricultural soil and freshwater environments in the upper irrigation area of the Yellow River.

Agricultural activities are among the most significant sources of microplastics (MPs) in water. However, few studies have explored the effect of irrigation on the fate of MPs in agricultural systems. This study investigated the distribution of MPs in agricultural soil, surface water, and sediment of adjacent rivers, as well as the "MP communities" in various environments before and after irrigation in a typical agricultural irrigation area of the Yellow River. MPs were detected in all of the examined sites. The number of MPs in surface water and sediment increased after irrigation, whereas those in the surface soil of croplands decreased. In the vertical direction, irrigation accelerated the migration of MPs (< 100 µm) deep into the soil. The vertical mobility of fibers in soil was faster than that of other types of MPs. Moreover, irrigation decreased the correlation between soil properties and MPs in soils. MP community analysis indicated that irrigation enhanced the differences between MP communities among adjacent environments. Collectively, our findings confirmed that river water irrigation caused secondary MP pollution in the soil environment and accelerated MP pollution in deep soil. Therefore, this study provides a theoretical basis for the development of strategies for MP pollution control in agricultural soil.

Removal and Mechanism of Cadmium, Lead and Copper in Water by Functional Modification of Silkworm Excrement Biochar.

A new type of biochar, called GBC, was prepared from silkworm excrement, and then modified by chitosan combined with pyromellitic dianhydride. The removal of mono-metal and polymetals (Pb, Cd and Cu) from an aqueous solution by GBC was investigated in this research. Compared to unmodified biochar, the removal rate of Pb and Cd by GBC was about 12% higher, while that of Cu was about 94.6% higher. It also shows the types of functional groups in biochar have a great impact on their adsorption. The removal of Pb is mainly involved in the N-C=O functional group, the removal of Cd is mainly involved in N-containing functional group and C=C bond, and that of Cu is mainly involved in N-containing functional group, carboxyl group, hydroxyl group, and a carbonyl group. Five adsorption-desorption cycles of GBC were carried out, and it was found that the adsorption capacities of GBC for Pb, Cd and Cu decreased by 7.28%, 10.78% and 6.07%, respectively, indicating that GBC had a good renewable performance. The adsorption capacity of GBC for Cu in different water samples is between 89.62 and 93.47 mg·g-1, indicating that GBC has great application potential for the removal of Cu in wastewater.

Spatial variability of microplastic pollution on surface of rivers in a mountain-plain transitional area: A case study in the Chin Ling-Wei River Plain, China.

Inland lakes and rivers are large reservoirs of microplastics. But currently, not too much research was done on microplastics of mountain rivers. The protection of water sources from microplastics is extremely significant for the safety of human drinking water. We quantified the distribution and variation of microplastics in the surface water from tributary (upstream water-source regions) to main stream (human settlements) in the Chin Ling-Wei River Plain Rivers, and assessed the pollution risk. Rivers in the Chin Ling-Wei River Plain contained various levels of microplastics (2.30-21.05 items/L), and the main stream of the river contained higher concentrations most commonly of microplastics than tributaries. The microplastics were fragments and films; they constituted 82.3% of the total abundance of microplastics. Microplastics with a particle size < 500 µm accounted for 64.3% of all the samples. As rivers flow from the mountains to the plains, the land-use types along the rivers become more multifunctional. Thus, the risk of river microplastic pollution increases sharply with distance downstream. Our research explored the microplastics pollution in the Chin Ling mountains based on topography and land-use types and thus provides a reference for further studies exploring the spatial distribution characteristics of microplastics in small-scale rivers and for pollution risk assessments.

Spatial distribution and human health risk assessment of soil heavy metals based on sequential Gaussian simulation and positive matrix factorization model: A case study in irrigation area of the Yellow River.

The content of Cd, Cu, Pb, Zn, Cr, Ni and As from 250 soil samples was measured in agricultural soil of Ningxia section of the Yellow River. Positive matrix factorization (PMF) was to identify the main sources of these heavy metals; Sequential Gaussian Simulation (SGS) was to identify their spatial distribution and high-risk areas; and Human Health risk (HHR) model was to measure the health risk. Results showed that the average content of Cd and As exceeds the risk screening value of "Soil Environmental Quality-Agricultural Land Soil Pollution Risk Control Standard" (GB 15618-2018), which belongs to slight-level pollution. Although the content of other types of HMs (Cu, Pb, Zn, Cr, Ni) is below the risk screening value, they are still included heavily in the soil (except Cr). PMF indicated that mixed sources of agriculture and industry accounted for 27.06%, natural sources accounted for 14.12%, industrial sources accounted for 23.04%, traffic sources accounted for 21.50%, and Yellow River sedimentary sources accounted for 14.28%. PMF-HHR showed that the mixed sources of agriculture and industry are the most important factor causing non-carcinogenic risk (HI) to children (accounting for 55.75%). Industrial sources and traffic sources were the two main factors that cause HI to adults (industrial sources accounted for 25.16%, and traffic sources accounted for 28.78%). Mixed sources of agriculture and industry and natural sources were the two main factors that cause carcinogenic risk (CR) (mixed sources of agriculture and industry account for 35.34%, and natural sources account for 33.23%). SGS indicated that 0.64% and 9.32% of the total areas were posing as higher HI areas to children and adults respectively; in particular, 0.68% and 1.12% of the areas were identified as higher HI of As and Cr areas at a critical probability of 0.9.