Mechanical activation-enhanced metal-organic coordination strategy to fabricate high-performance starch/polyvinyl alcohol films by extrusion blowing.

The production of high-performance starch-based packaging films by extrusion blowing is challenging, ascribed to poor processability of the blend precursors. In this study, a new strategy of mechanical activation (MA)-enhanced metal-organic coordination was proposed to improve the processability of starch (St)/polyvinyl alcohol (PVA) blend precursor, with calcium acetate (CA) as a chelating agent and glycerol as a plasticizer. MA pretreatment activated the hydroxyl groups of starch and PVA for constructing strong metal-organic coordination between CA and St/PVA during reactive extrusion, which effectively enhanced the melt processing properties of the blend precursor, contributing to the fabrication of high-performance St/PVA films by the extrusion-blowing method. The as-prepared St/PVA films exhibited excellent mechanical properties (tensile strength of 34.5 MPa; elongation at break of 271.8 %), water vapor barrier performance (water vapor permeability of 0.704 × 10-12 g·cm-1·s-1·Pa-1), and oxygen barrier performance (oxygen transmission rate of 0.7 cm3/(m2·day·bar)), along with high transmittance and good uniformity. These outstanding characteristics and performances can be attributed to the improved interfacial interaction and compatibility between the two matrix phases. This study uncovers the mechanism of MA-enhanced metal-organic coordination for improving the properties of starch-based films, which provides a convenient and eco-friendly technology for the preparation of high-performance biodegradable films.

Fabrication of biodegradable and cold-water-soluble starch/polyvinyl alcohol films as inner packaging materials of pesticides: Enhanced emulsification, dispersibility, and efficacy.

Developing environmentally friendly film materials for packaging pesticides is significant yet challenging. The use of native starch for preparing inner packaging materials of pesticides is limited by its physicochemical properties. In this study, a novel strategy of synergetic mechanical activation (MA)-enhanced solid-phase esterification of starch and cooperative combination of starch and polyvinyl alcohol (PVA) was proposed to fabricate biodegradable and cold-water-soluble starch (St)/PVA films. The appropriate esterification of starch and favorable compatibility between starch and PVA contributed to the production of St/PVA films by the extrusion-blowing method. The as-prepared film with St/PVA ratio of 4:6 exhibited outstanding mechanical properties (tensile strengths of 21.0 MPa; elongation at break of 213.9 %), cold-water solubility (dissolution time of 90 s), and oxygen barrier performance (oxygen transmission rate of 1.41 cm3/(m2·day·bar)). The dissolved St/PVA films with amphiphilic groups were conducive to the emulsification of butachlor (a fat-soluble liquid pesticide) and the dispersibility of oxyfluorfen (a fat-soluble solid pesticide). Furthermore, a mechanism of the interaction between pesticides and the surface of weed leaves was proposed to reveal the enhanced efficacy of St/PVA films-packaged pesticides. The strategy based on MA-enhanced esterification and PVA blending is efficient to produce starch-based films suitable for inner packaging materials of pesticides.

Fabrication of a poly(N-isopropylacrylamide)-grafted alginate composite aerogel for efficient treatment of emulsified oily wastewater.

The treatment of emulsion wastewater poses significant challenges. In this study, a novel porous material, namely esterified bagasse/poly(N, N-dimethylacrylamide)/sodium alginate (SBS/PDMAA/Alg) aerogel, was developed for efficient demulsification and oil recovery. By grafting a poly(N-isopropylacrylamide) (PNIPAM) brush onto the SBS/PDMAA/Alg skeleton through free radical polymerization, the resulting aerogel exhibits both surface charge and a molecular brush structure. The aerogel demonstrates remarkable demulsification efficiency for cationic surfactant-stabilized emulsions at various concentrations, achieving a demulsification efficiency of 95.6% even at an oil content of 100 g L-1. Furthermore, the molecular brush structure extends the application range of the aerogel, enabling a demulsification efficiency of 98.3% for anionic and non-ionic surfactant-stabilized emulsions. The interpenetrating polymer network (IPN) structure formed by SBS, PDMAA, and alginate enhances the mechanical stability of the aerogel, enabling a demulsification efficiency of 91.3% even after 20 repeated cycles. The demulsification ability of the composite aerogel is attributed to its surface charge, high interfacial activity, and unique brush-like structure. A demulsification mechanism based on the synergistic effect of surface charge and molecular brush is proposed to elucidate the efficient demulsification process.

Direct and efficient conversion of cellulose to levulinic acid catalyzed by carbon foam-supported heteropolyacid with Brønsted-Lewis dual-acidic sites.

This study aimed to produce bio-based levulinic acid (LA) via direct and efficient conversion of cellulose catalyzed by a sustainable solid acid. A carbon foam (CF)-supported aluminotungstic acid (HAlW/CF) catalyst with Brønsted-Lewis dual-acidic sites was creatively engineered by a hydrothermal impregnation method. The activity of the HAlW/CF catalyst was determined via the hydrolysis and conversion of cellulose to prepare LA in aqueous system. The cooperative effect of Brønsted and Lewis acids in HAlW/CF resulted in high cellulose conversion (89.4%) and LA yield (60.9%) at 180 °C for 4 h, which were greater than the combined catalytic efficiencies of single HAlW and CF under the same conditions. The HAlW/CF catalyst in block form exhibited superior catalytic activity, facile separation from reaction system, and favorable reusability. This work offers novel perspectives for the development of recyclable dual-acidic catalysts to achieve one-pot catalytic conversion of biomass to value-added chemicals.

Fast-thermoresponsive carboxylated carbon nanotube/chitosan aerogels with switchable wettability for oil/water separation.

The use of aerogels to selectively recover oil from oily wastewater is effective but challenging. In this study, a new carboxylated carbon nanotube/chitosan aerogel (CCNT/CA) with switchable wettability was developed as a smart adsorbent for fast oil absorption and oil recovery. Vinyltrimethoxysilane and thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) was grafted onto the surface of the CCNT/CA skeleton, and the resulting smart aerogel (PNI-Si@CCNT/CA) exhibited temperature responsiveness. PNI-Si@CCNT/CA exhibited an excellent reversible conversion between hydrophilicity and hydrophobicity when the temperature was changed to below or above the lower critical solution temperature (LCST) of PNIPAAm (~32 °C). Most importantly, CCNT significantly increased the oil absorption capacity, improved the mechanical properties, accelerated phonon conduction, enhanced thermal conductivity (80.57 mW m-1 K-1), improved the temperature response rate, shortened the oil desorption time (15 min), and improved the oil/water separation efficiency of PNI-Si@CCNT/CA because a strong interface interaction occurred between CCNT and chitosan. Moreover, PNI-Si@CCNT/CA absorbed oil at 45 °C and released the absorbed oil at 25 °C. It maintained its good adsorption performance after 15 cycles, and this was ascribed to its excellent mechanical properties and stable structure.

Fabrication of a CO2-responsive chitosan aerogel as an effective adsorbent for the adsorption and desorption of heavy metal ions.

In the traditional desorption method, strong acid is commonly used as an eluent for the regeneration of adsorbents. It is of critical economic and environmental significance to develop a chemical-free desorption method. In this study, a new CO2-responsive chitosan aerogel adsorbent was synthesized from CO2-responsive poly(acrylic acid-2-(dimethylamino)ethyl methacrylate) and chitosan by physicochemical double crosslinking for the adsorption of Cu2+. Compared with the chitosan aerogel, the adsorption capacity of Cu2+ and mechanical properties of CO2-responsive chitosan aerogel increased by 162% and 660%, respectively. Most importantly, after the adsorption of Cu2+ by CO2-responsive chitosan aerogel, the Cu2+ could be desorbed by CO2 bubbling, and the desorption rate of metal ions was more than 80%. The adsorption of Cu2+ by aerogel was attributed to chelation and complexation. The desorption of porous chitosan/P(AA-co-DMAEMA) aerogels (CPA) by CO2 mainly occurred through charge repulsion of protonated ‒NH2 and ‒N‒ groups. After 6 cycles, the adsorption capacity of CPA for metal ions still reached 70% of the initial adsorption capacity, and the desorption rate reached 75%. This novel CO2-responsive chitosan aerogel is a highly efficient and environmentally friendly adsorbent for the adsorption and recovery of metal ions.

Enhancement of hydrothermal carbonization of chitin by combined pretreatment of mechanical activation and FeCl3.

In this work, a combined mechanical activation and FeCl3 (MA + FeCl3) method was applied to pretreat chitin to enhance the degree of hydrothermal carbonization. MA + FeCl3 pretreatment significantly disrupt the crystalline region of chitin and Fe3+ entered into the molecular chain, resulting in the destruction of the stable structure of chitin. The chemical and structural properties of hydrochars were characterized by EA, SEM, FTIR, XRD, XPS, 13C solid state NMR, and N2 adsorption-desorption analyses. The results showed that the H/C and O/C atomic ratios of HC-MAFCT/230 (the hydrochar derived from MA + FeCl3 pretreated chitin with hydrothermal reaction temperature of 230 °C) were 0.96 and 0.34, respectively. Van Krevelen diagram indicated that the hydrothermal carbonization of chitin underwent a series of reactions such as dehydration, decarboxylation, and aromatization. HC-MAFCT/230 had abundant oxygen- and nitrogen-containing functional groups. HC-MAFCT/230 exhibited a porous structure, with the specific surface area of 128 m2 g-1, which was a promising carbon material.

A stepwise processing strategy for treating highly acidic wastewater and comprehensive utilization of the products derived from different treating steps.

A stepwise processing strategy, including initial neutralization, chemical mineralization, and complete neutralization treating steps, was developed to effectively treat and utilize the highly acidic wastewater derived from titanium dioxide production. Approximately 94.6% of SO42-, 100% of Fe, and most of other metals were recovered to produce white gypsum, schwertmannite, and Fe0/Fe3O4@biochar (Fe0/Fe3O4@BC) composite in the corresponding treating steps. The resulting effluent with neutral pH and a small amount of metal ions could be discharged to general sewage treatment plant for further processing. Schwertmannite was applied as a heterogeneous Fenton-like catalyst to stimulate H2O2 to produce active radicals for effective degradation and mineralization of methyl orange (MO) in solution. The MO removal of 100% and total organic carbon removal of 91.1% were achieved in schwertmannite/H2O2 reaction system, and schwertmannite exhibited good stability and reusability. Fe0/Fe3O4@BC composite was applied to remove Cr(VI), with the adsorption capacity of 67.74 mg g-1. The removal of Cr(VI) using Fe0/Fe3O4@BC composite was a chemisorption process, including the adsorption of Cr(VI), reduction of Cr(VI) to Cr(III), and co-precipitation of Cr(III)/Fe(III) oxides/hydroxides. This stepwise treating strategy is a promising technology for effective treatment of highly acidic industrial wastewater and comprehensive utilization of the related products.

3D porous tubular network-structured chitosan-based beads with multifunctional groups: Highly efficient and selective removal of Cu2.

Herein, an effective adsorbent, 3D porous tubular network-structured citric acid-chitosan/Fe/polyethyleneimine beads (CCFPB) with multifunctional active groups and strong selectivity, was prepared for the selective removal of Cu2+ from simulated wastewater. Compared with pure chitosan beads (CB), the adsorption capacity of CCFPB for Cu2+ was increased by 127 mg g-1 (238%), and the adsorption equilibrium time was shortened by 480 min. The CCFPB showed porous surface and a novel 3D porous tubular network structure in interior, which were benefit to the diffusion of Cu2+ from surface to interior of the CCFPB and the shortening of adsorption equilibrium time. The common coexisting ions in the simulated wastewater had almost no effect on the adsorption of Cu2+ by CCFPB, and the adsorption was fast and reached equilibrium within 10 h. The adsorption process followed pseudo-second-order kinetics and the Langmuir isotherm model (qm = 240.9 mg g-1 for Cu2+). The adsorption mechanism of CCFPB for Cu2+ was mainly the synergistic interaction with amino, carboxyl, and hydroxyl groups. This strategy shows great potential for developing a variety of novel, highly active, and reusable immobilized functional beads materials for effective separation of Cu2+ from multi-ion wastewater.

Preparation of sugarcane bagasse succinate/alginate porous gel beads via a self-assembly strategy: Improving the structural stability and adsorption efficiency for heavy metal ions.

Sugarcane bagasse, a kind of agricultural waste, was esterified by mechanical activation-assisted solid phase reaction with succinic anhydride as esterifying agent to prepare SB succinate (SBS) with rich carboxyl and ester functional groups. The layer-by-layer (LbL) self-assembly technology was used to prepare SBS/alginate (Alg) porous gel beads (SAPGB) with outstanding mechanical strength and desired porous structure from external surface to interior through the formation of gel network structure of SBS/Ca2+/Alg. The adsorption kinetics and isotherm indicated that the adsorption of metal ions onto SAPGB followed the pseudo-second-order kinetics and Langmuir isotherm mode (Qmax = 354.60 and 176.36 mg g-1 for Pb2+ and Cd2+, respectively). The adsorption behavior of SAPGB for metal ions was mainly amonolayer chemical adsorption process. The adsorption was fast and reached equilibrium within 60 min, ascribed to rapid diffusion from porous surface into internal pores. In addition, the stable SAPGB adsorbent exhibited excellent regeneration performance.

Effective treatment and utilization of hazardous waste sulfuric acid generated from alkylation by lignocellulose ester-catalyzed oxidative degradation of organic pollutants.

Alkylation reaction catalyzed by concentrated H2SO4 generates hazardous waste H2SO4 containing a large amount of organic pollutants. This study focused on effective utilization and treatment of the waste H2SO4 for simultaneous consumption of H2SO4 and deep oxidative degradation of the organics. The waste H2SO4 could completely react with magnesium oxide ore to prepare crude MgSO4 solution, and the organic pollutants in the solution were deeply degraded and mainly mineralized to H2O and CO2 with H2O2 as oxidant and sugarcane bagasse citrate (SBC), a kind of lignocellulose ester, as catalyst. The total amount of acidic groups of SBC significantly affected its catalytic activity, attributing to that these oxygen-containing functional groups adsorbed and immobilized metal ions on SBC to form catalytic active sites, which could activate and catalyze H2O2 to generate •OH and HO2• radicals for effective degradation of the organics. The resulting purified MgSO4 solution with color removal of 93.71% and total organic carbon removal of 85.89% under optimum catalytic reaction conditions was used to produce qualified MgSO4∙7H2O product. These results highlighted the feasibility of using lignocellulose ester as effective catalyst for deep oxidative degradation of hazardous organic pollutants.

Preparation of a Stable Nanoscale Manganese Residue-Derived FeS@Starch-Derived Carbon Composite for the Adsorption of Safranine T.

To develop a novel, low-cost adsorbent with natural material and industrial waste as raw materials, nanoscale manganese residue-derived FeS@starch-derived carbon (MR-FeS@SC) composite was prepared by the carbonization of starch-manganese residue gel. Manganese residue-derived FeS (MR-FeS) and starch-derived carbon (SC) were also prepared as contrasts for comparative studies. The MR-FeS@SC nanocomposite exhibited relatively large specific surface area and micropore volume, appropriate pore size, abundant functional groups, strong interaction between the functional groups of SC and MR-FeS, and the immobilization and uniform distribution of MR-FeS nanoparticles onto SC support material, which contributed to better adsorption properties for the removal of Safranine T (ST) from the aqueous solution compared with those of MR-FeS and SC. The adsorption could be conducted at a wide range of pH and temperature to achieve a satisfy removal efficiency of ST with MR-FeS@SC nanocomposite as adsorbent. The adsorption kinetics well followed the pseudo-second-order model, and the dominant mechanism was chemisorption. The adsorption behavior was well described by the Langmuir isotherm model. Due to the strong interaction between MR-FeS nanoparticles and SC support, MR-FeS@SC nanocomposite exhibited better reusability and stability even after fifteen cycles. This study provides a facile method of preparing effective and stable adsorbents for the treatment of dye wastewater.

Fabrication of graphite/MgO-reinforced poly(vinyl chloride) composites by mechanical activation with enhanced thermal properties.

In this study, a mechanical activation (MA) approach was developed to fabricate graphite/MgO-reinforced poly(vinyl chloride) (PVC) composites with superior thermal properties. The composites were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and differential thermogravimetric (DTG) analysis. SEM results revealed uniformly dispersed graphite and MgO flakes in a PVC matrix and the successful formation of a thermal network by MA, which led to enhanced thermal conductivity. DSC and TGA results of the composites showed enhancement in the glass transition temperature (Tg) from 82.81 °C to 88.60 °C and decomposition temperature from 287.61 °C to 305.59 °C as compared to pristine PVC. The thermal conductivity of the graphite/MgO/PVC composite at optimum conditions was 0.8791 W m-1 K-1, which was 6.27 times higher than that of pristine PVC. The mechanical properties such as the tensile strength and bending strength of graphite/MgO/PVC composites were also augmented as compared to pristine PVC, graphite/PVC and MgO/PVC composites. Due to the enhanced thermal properties of the newly designed graphite/MgO/PVC composites, they have potential as alternatives to classical PVC-based materials in thermal and many other target field-based applications.

Mineralization of organics in hazardous waste sulfuric acid by natural manganese oxide ore and a combined MnO2/activated carbon treatment to produce qualified manganese sulfate.

To effectively dispose and utilize the hazardous waste H2SO4 generated from alkylation, an environmentally friendly and feasible technology for the simultaneous oxidative degradation of organics and consumption of H2SO4 was developed. Pyrolusite, a natural manganese oxide ore, was used for the oxidative degradation and mineralization of the organics, and reduction leaching of Mn from the pyrolusite occurred simultaneously. The total organic carbon (TOC) removal and Mn leaching efficiency were 46% and 16.44%, respectively. In addition, pyrites was applied as a reductant to extract Mn from the pyrolusite, and an Mn leaching efficiency of 98.31% was obtained under the optimized conditions of 4/1 liquid/solid ratio, 350 rpm stirring speed, 1.5 mol L-1 H2SO4 concentration, and 95 °C for 1 h in the first oxidative degradation stage and a molar ratio of FeS2/MnO2 of 0.55/1 for 4 h in the reduction leaching stage. Subsequently, a combined treatment of MnO2/activated carbon was developed for further oxidation and adsorption of the organics in the solution, with the TOC removal of 84.11%. The resulting purified MnSO4 solution was concentrated to produce qualified MnSO4∙H2O, which met the requirements of an industrial product. This technology showed application potential in highly-efficient removal of hazardous organic contaminates.

Direct production of cellulose laurate by mechanical activation-strengthened solid phase synthesis.

This work reports that cellulose laurate could be directly produced by mechanical activation-strengthened solid phase synthesis (MASPS) in a customized stirring mill with using bagasse pulp and lauric acid as materials in an environmentally friendly way. Cellulose laurates with different degree of substitution were obtained under different synthesis conditions without the use of organic co-reagents and solvents. The characterization results showed that cellulose laurates had great changes in surface morphologies and crystal structures compared with bagasse pulp because of the intense milling and introduction of laurate groups, but still retained the cellulose I crystalline form of the native cellulose. MASPS could be considered as a simple, efficient and green method for the production of long chain cellulose esters.