Construction of a Two-Dimensional GO/Ti3C2TX Composite Membrane and Investigation of Mg2+/Li+ Separation Performance.

Graphene oxide (GO) two-dimensional (2D) membranes with unique layer structures and tunable layer spacing have special advantages and great potential in the field of water treatment. However, GO membranes face the issues of weak anti-swelling ability as well as poor permeability. We prepared GO/Ti3C2TX 2D composite membranes with 2D/2D structures by intercalating Ti3C2TX nanosheets with slightly smaller sizes into GO membranes. Ti3C2TX intercalation can effectively expand the layer spacing of GO, thereby substantially enhancing the flux of the composite membrane (2.82 to 6.35 L·m-2·h-1). Moreover, the GO/Ti3C2TX composite membrane exhibited a good Mg2+/Li+ separation capability. For the simulated brine, the separation factor of M2 was 3.81, and the salt solution flux was as high as 5.26 L·m-2·h-1. Meanwhile, the incorporation of Ti3C2TX nanosheets significantly improved the stability of GO/Ti3C2TX membranes in different pH environments. This study provides a unique insight into the preparation of highly permeable and ion-selective GO membranes.

Engineered hydrochar from waste reed straw for peroxymonosulfate activation to degrade quinclorac and improve solanaceae plants growth.

Hydrochar from agricultural wastes is regarded as a prospective and low-cost material to activate peroxymonosulfate (PMS) for degrading pollutants. Herein, a novel in-situ N-doped hydrochar composite (RHCM4) was synthesized using montmorillonite and waste reed straw rich in nitrogen as pyrolysis catalyst and carbon source, respectively. The fabricated RHCM4 possessed excellent PMS activation performance for decomposing quinclorac (QC), a refractory herbicide, with a high removal efficiency of 100.0% and mineralization efficiency of 75.1%. The quenching experiments and electron spin resonance (ESR) detection disclosed free radicals (•OH, •SO4-, and •O2-) and non-radicals (1O2) took part in the QC degradation process. Additionally, the catalytic mechanisms were analyzed in depth with the aid of various characterizations. Moreover, the QC degradation intermediates and pathways were clarified by density functional theory calculations and HPLC-MS. Importantly, phytotoxicity experiments showed that RHCM4/PMS could efficaciously mitigate the injury of QC to Solanaceae crops (pepper, tomato, and tobacco). These findings give a new idea for enhancing the catalytic activity of hydrochar from agricultural wastes and broaden its application in the field of agricultural environment.

Cellulose esterification with carboxylic acid in deep eutectic solvent pretreatment inhibits enzymatic hydrolysis.

Avicel cellulose was pretreated using two commonly used carboxylic acid-based deep eutectic solvents, i.e., choline chloride-lactic acid and choline chloride-formic acid. The pretreatment process resulted in the formation of cellulose esters with lactic acid and formic acid, which was confirmed by infrared and nuclear magnetic resonance spectra. Surprisingly, the esterified cellulose led to a significant decrease in the 48-h enzymatic glucose yield (≥75%) compared to raw Avicel cellulose. Analysis of changes in cellulose properties caused by pretreatment, including crystallinity, degree of polymerization, particle size and cellulose accessibility, contradicted the observed decline in enzymatic cellulose hydrolysis. However, removing the ester groups through saponification largely recovered the reduction in cellulose conversion. The decreased enzymatic cellulose hydrolysis by esterification may be attributed to changes in the interaction between cellulose-binding domain of cellulase and cellulose. These findings provide valuable insights into improving the saccharification of lignocellulosic biomass pretreated by carboxylic acid-based DESs.

Efficiency Recycling and Utilization of Phosphate from Wastewater Using LDHs-Modified Biochar.

The excessive application of phosphate fertilizers easily causes water eutrophication. Phosphorus recovery by adsorption is regarded as an effective and simple intervention to control water bodies' eutrophication. In this work, a series of new adsorbents, layered double hydroxides (LDHs)-modified biochar (BC) with different molar ratios of Mg2+ and Fe3+, were synthesized based on waste jute stalk and used for recycling phosphate from wastewater. The prepared LDHs-BC4 (the molar ratio of Mg/Fe is 4:1) has significantly high adsorption performance, and the recovery rate of phosphate is about 10 times higher than that of the pristine jute stalk BC. The maximum adsorption capacity of LDHs-BC4 for phosphate was 10.64 mg-P/g. The main mechanism of phosphate adsorption mainly includes electrostatic attraction, ion exchange, ligand exchange, and intragranular diffusion. Moreover, the phosphate-adsorbed LDHs-BC4 could promote mung bean growth, which indicated the recovery phosphate from wastewater could be used as a fertilizer.

Environmental-friendly hydrochar-montmorillonite composite for efficient catalytic degradation of dicamba and alleviating its damage to crops.

In recent years, carbon-based materials catalyzing peroxymonosulfate (PMS) for green degradation of persistent organic pollutants have attracted increasing attention. However, PMS activation by hydrochar composite (e.g. hydrochar-montomorillonite) has rarely been investigated. Herein, a simple preparation, low-cost and eco-friendly catalyst of hydrochar-montmorillonite composite (HC-Mt) was prepared to firstly catalyze PMS for the degradation of dicamba (DIC). The as-prepared HC-Mt showed a remarkably better catalyzing performance for PMS than pure hydrochar (HC) due to its good physicochemical characteristics and abundant oxygen-containing groups. Furthermore, the electron spin resonance (ESR) and quenching tests revealed that active species such as SO4-, OH and O2- all participated in the degradation process. DIC sites on C6, Cl 10, and O15 exhibited higher reactivity according to the density functional theory (DFT) calculation, which were easily attacked by active species. The DIC degradation mainly occurred via hydroxyl substitution, decarboxylation, oxidation and ring-cleavage and finally most of the intermediates were mineralized into CO2 and H2O. Finally, the phytotoxicity assessment was measured by the germination growth situation of tobacco and mung beans in the presence of DIC (with or without treatment by HC-Mt/PMS). The result showed that HC-Mt/PMS could significantly reduce the phytotoxicity of DIC to crops, suggesting that catalyzing PMS using HC-Mt was environmentally friendly. Therefore, this work did not only provide a novel catalyzing PMS strategy using hydrochar composite for wastewater treatment, but also give a new idea for herbicide phytotoxicity management.

Application of 3D magnetic nanocomposites: MXene-supported Fe3O4@CS nanospheres for highly efficient adsorption and separation of dyes.

Due to the presence of several hydroxyl and amino groups on the surface, chitosan (CS) has been reported to be a potential candidate to solve the pollution caused by dyes in different industrial wastewater. However, it is associated with the recycling issues. Nano-Fe3O4 has the advantages of easy magnetic separation and surface functionalization, which can improve the efficiency as well as selectivity of separation. However, its tendency for agglomeration can reduce the adsorption capacity. MXene can provide suitable support for both CS and Fe3O4 to construct new MXene@Fe3O4@CS composites. In this study, MXene@Fe3O4@CSmagnetic nanosphere was synthesized by ultrasonic self-assembly to remove Congo red (CR). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier Transform Infrared (FT-IR) spectroscopy were employed to characterize the nanocomposites. According to the batch experiments, the adsorption kinetics were found to predominantly follow quasi-secondary rate kinetics. The adsorption followed Langmuir isotherm model. The adsorption process was found to be endothermic, entropy-driven, and thermodynamically spontaneous process. The adsorption capacity for CR was estimated as 620.22 mg·g-1.

Airflow Synergistic Needleless Electrospinning of Instant Noodle-like Curly Nanofibrous Membranes for High-Efficiency Air Filtration.

Particulate matter (PM) pollution has become a serious environmental concern. Nanofibrous filters are widely reported to remove PM from polluted air. Herein, efficient and lightweight PM air filters are presented using airflow synergistic needleless electrospinning composed of auxiliary fields such as an airflow field and a secondary inductive electric field. Compared to needleless electrospinning with other spinnerets, it significantly improves productivity, fiber diameter, and porosity of fibrous air filters. The instant noodle-like nanofiber structure can also be controlled by adjusting the airflow velocity. These air filters exhibit high (2.5 µm particulate matter) PM2.5 removal efficiency (99.9%) and high (0.3 µm particulate matter) PM0.3 removal efficiency (99.1%), low pressure drop (56 Pa for PM2.5 and 78 Pa for PM0.3 ), and large dust holding capacitance (the maximum value is 168 g m-2 for PM2.5 , while 102 g m-2 for PM0.3 ). Meanwhile, the proposed PM filters are also tested suitable and stable to other polluted air filtrations such as cigarette smoke and sawdust. The large-scale synthesis of such an attractive nanofiber structure presents the great potential of high-performance filtration/separation materials.

Robust super-hydrophobic/super-oleophilic sandwich-like UIO-66-F4@rGO composites for efficient and multitasking oil/water separation applications.

Super-wetting MOFs@graphene hybrid has shown promising application for oil/water separation, due to high porosity, low density, and controllable wettability, however, achieving excellent stability and recyclability are found to be still challenging. In this study, sandwich-like UIO-66-F4@rGO hybrid was synthesized by immobilization of UIO-66-F4 nanoparticles on rGO matrix, which featured the unique micro/nano hierarchy with hydrophobic characteristics. In order to realize the oil/water separation, as-prepared sandwich-like UIO-66-F4@rGO hybrid was applied as a potential candidate for constructing robust super-hydrophobic/super-oleophilic interfaces by using filter paper (FP) and melamine sponge (MS) as substrates. Typically, the surface modification of substrates can be easily achieved by simple dip-coating method, and interfacial adhesion between substrates and UIO-66-F4@rGO was enhanced by cross-linking of hydroxyl-fluoropolysiloxane (FPSO). Consequently, the super-hydrophobic/oleophilic UIO-66-F4@rGO/FP exhibited high contact angle of 169.3 ± 0.6° and was capable of separating various water-in-oil emulsions effectively. The flux and separation efficiency were 990.45 ± 36.28 Lm-2 h-1 and 99.73 ± 0.19 % driven by gravity, respectively. The super-hydrophobic/super-oleophilic UIO-66-F4@rGO/MS possessed selective oil absorption with absorption capacity of 26∼61 g/g depending on the viscosity of oils and continuous cleaning of oil spill. Furthermore, the UIO-66-F4@rGO composite could tolerate high/low temperature, corrosive solutions, and physical damage, displaying robust and stable super-hydrophobic/super-oleophilic interfaces for treating oily wastewater in harsh environments.

Attached ß-cyclodextrin/γ-(2,3-epoxypropoxy) propyl trimethoxysilane to graphene oxide and its application in copper removal.

The environmental applications of graphene oxide and ß-cyclodextrin (ß-CD) have attracted great attention since their first discovery. Novel nanocomposites were successfully prepared by using an esterification reaction between ß-cyclodextrin/γ-(2,3-epoxypropoxy) propyl trimethoxysilane grafted graphene oxide (ß-CD/GPTMS/GO). The ß-CD/GPTMS/GO nanocomposites were used to remove the Cu2+ from aqueous solutions. The characteristics of ß-CD/GPTMS/GO were detected by scanning electron microscopy (SEM), Fourier transform infrared, X-ray diffraction (XRD), thermogravimetric analysis (TG) and energy dispersive X-ray (EDX). The dispersibility of graphene oxide was excellent due to the addition of ß-CD. The adsorption isotherms data obtained at the optimum pH 7 were fitted by Langmuir isotherm model. The excellent adsorption properties of ß-CD/GPTMS/GO for Cu2+ ions could be attributed to the apolar cavity structure of ß-CD, the high surface area and abundant functional groups on the surface of GO. The adsorption patterns of ß-CD/GPTMS/GO were electrostatic attraction, formation of host-guest inclusion complexes and the ion exchange adsorption. The efficient adsorption of ß-CD/GPTMS/GO for Cu2+ ions suggested that these novel nanocomposites may be ideal candidates for removing other cation pollutants from waste water.

Novel polyvinylidene fluoride nanofiltration membrane blended with functionalized halloysite nanotubes for dye and heavy metal ions removal.

Membrane separation is an effective method for the removal of hazardous materials from wastewater. Halloysite nanotubes (HNTs) were functionalized with 3-aminopropyltriethoxysilane (APTES), and novel polyvinylidene fluoride (PVDF) nanofiltration membranes were prepared by blending with various concentrations of APTES grafted HNTs (A-HNTs). The morphology structure of the membranes were characterized by scanning electron microscope (SEM) and atomic force microscopy (AFM). The contact angle (CA), pure water flux (PWF) and antifouling capacity of membranes were investigated in detail. In addition, the separation performance of membranes were reflected by the removal of dye and heavy metal ions in simulated wastewater. The results revealed that the hydrophilicity of A-HNTs blended PVDF membrane (A-HNTs@PVDF) was enhanced significantly. Owing to the electrostatic interaction between membrane surface and dye molecules, the dye rejection ratio of 3% A-HNTs@PVDF membrane reached 94.9%. The heavy metal ions rejection ratio and adsorption capacity of membrane were also improved with the addition of A-HNTs. More importantly, A-HNTs@PVDF membrane exhibited excellent rejection stability and reuse performances after several times fouling and washing tests. It can be expected that the present work will provide insight into a new method for membrane modification in the field of wastewater treatment.