Enlarged Pore Size Research Articles

Coupling activation and curing to tune the permselectivity of poly(piperazine amide) nanofiltration membranes

To tune both water transport and solute rejection (i.e., permselectivity) of nanofiltration (NF) membranes, polyamide (PA) films were synthesized under the same interfacial polymerization (IP) conditions following distinct posttreatments, and the underlying relationship between the PA structure and membrane performance was systematically investigated. The combination of hexane activation and water curing was the optimal posttreatment process, which significantly increased membrane permeability from 6.7 ± 0.4 to 19.8 ± 0.8 L·m−2·h−1·bar−1 and enhanced the selectivity of NaCl/Na2SO4 from 9.6 ± 1.2 to 45.8 ± 0.8. For this combined posttreatment process, the outstanding permeability was due to the enlarged PA film pore size, the enhanced hydrophilicity and the reduced PA thickness and crosslinking degree, and the high NaCl/Na2SO4 selectivity was attributed to the increased electrostatic repulsion between the hydrolyzed acyl chloride groups (i.e., carboxyl groups) and divalent anions. Furthermore, a continuous filtration of 10 days was implemented, and the permeation flux and salt rejection trends for the fabricated PA membranes were maintained at high levels, which indicated excellent long-term stability for the combined posttreatment process. The results of the current study are of paramount practical significance for the reconciliation of permeability and selectivity in water treatment and resource recovery from wastewater.

Microstructural investigation into the damage behaviour of MX80 bentonite pellet under wetting/drying path using Mercury Intrusion Porosimetry (MIP) and Micro-Computed Tomography (μCT)

MX80 bentonite pellet has been considered as a promising sealing/backfilling material in geological disposal facilities for high-level and intermediate-level radioactive wastes. As the sealing/backfilling material which is subjected to hydration by pore water or vapour from host rock can be damaged by wetting-induced cracking, it is essential to clarify the suction effect on the damage behaviour of the material. In this study, a combined Mercury Intrusion Porosimetry/Micro-Computed Tomography (MIP/μCT) method was applied to investigate the microstructural damage of the MX80 bentonite cylinder-shaped 32-mm pellets equilibrated under suctions s from 113 to 1.5 MPa for wetting and from 113 to 262 MPa for drying. The enlarged pore size distribution (PSD) curves by MIP/μCT revealed an insignificant drying-induced closure of cracks, as opposed to massively developed wetting-induced cracks, with the size of the largest cracks reaching several millimetres. This is confirmed by the μCT observation. Indeed, the μCT images showed a negligible effect of drying on cracking, contrary to the effect of wetting characterised by significant cracking from the marginal area to the central part of pellet, indicating significant damage of pellet by wetting. Additionally, only horizontal cracks were identified at s ≥ 82 MPa. Vertical cracks emerged and propagated only at s ≤ 57 MPa, together with further expanding of horizontal cracks, due to the preferentially horizontal orientation of clay particles resulting from the one-dimensional compaction in the pellet fabrication. A damage coefficient D was defined as the ratio of the volume of macro-pores to the total volume of pellet. D increased slightly upon drying from suction 113 to 262 MPa and significantly upon wetting from suction 113 to 3.2 MPa, but kept almost unchanged when wetting furthered from suction 3.2 to 1.5 MPa because the clogging of macro-pores by the exfoliation effect slowed down the cracking rate.

Etched hollow periodic mesoporous organosilica with enlarged pore size for high-performance solid phase microextraction of polybrominated biphenyls

Hollow mesoporous silica has attracted increasing attention due to its outstanding characteristics such as low density, large void, mesoporous channel, and large specific surface area. Herein, a kind of etched hollow periodic mesoporous organosilica (EHPMOS) with enlarged mesopore size was successfully synthesized for high-performance solid phase microextraction (SPME). The etched silica material was prepared as a SPME fiber with uniform morphology, and the enrichment capacities for polybrominated biphenyls (PBBs) were systematically studied. In particular, the EHPMOS showed significant enrichment factors (158–9516) for PBBs. In addition, based on the home-made SPME fiber and gas chromatography-mass spectrometry (GC–MS), an ultra-sensitive analytical method was developed, with low limits of detection (0.11–0.32 ng·L-1), a wide linear range (1–1000 ng·L-1), and satisfactory reproducibility. And accurate quantifications of ultra-trace PBBs in environmental water sample were achieved.

Unveiling the role of post-treatment in thin-film composite nanofiltration membranes: Performance and mechanism

The deep role and mechanism of post-treatment in the morphology and performance of thin-film composite (TFC) nanofiltration (NF) membranes have rarely been revealed. In this work, four solutions of pure water, hexane, Na2CO3, and glycerol were selected for the post-treatment of TFC-NF membranes, and the performances of the resultant NF membranes were systematically investigated. The results showed that the hexane could effectively remove the residual acyl chloride groups and prevent the subsequent second growth of polyamide (PA) layers, thus leading to the formation of smoother and thinner PA membranes with higher water permeance and excellent salt rejections. Hydrolysis and swelling of unstable PA fragments in solutions (water, Na2CO3, and glycerin) contributed to greater negative charge, higher hydrophilicity, and enlarged pore size. The resultant NF membranes exhibited significantly enhanced water permeance and comparable separation behaviors to the control NF membrane. In addition, the well-constructed NF membranes possessed superior monovalent/multivalent ion selectivity, excellent antifouling, and stability. The mechanisms of the post-treatment on the performance enhancement of NF membranes were proposed from the perspective of interfacial interactions. The facile post-treatment strategy provides new insights into tailoring high-performance NF membranes for water treatment applications.

Efficient adsorption and photocatalytic degradation of water emerging contaminants through nanoarchitectonics of pore sizes and optical properties of zirconium-based MOFs

Over the past decades, the presence of pharmaceutical emerging contaminants in water bodies is receiving increasing attention due to the high concentration detected from wastewater effluent. Water systems contain a wide range of components coexisting together, which increases the difficulty of removing pollutants from the water. In order to achieve selective photodegradation and to enhance the photocatalytic activity of the photocatalyst on emerging contaminants, a Zr-based metal-organic framework (MOF), termed VNU-1 (VNU represents Vietnam National University) constructed with ditopic linker 1,4-bis(2-[4-carboxyphenyl]ethynyl)benzene (H2CPEB), with enlarged pore size and ameliorated optical properties, was synthesized and applied in this study. When compared to UiO-66 MOFs, which only had 30% photodegradation of sulfamethoxazole, VNU-1 had 7.5 times higher adsorption and reached 100% photodegradation in 10 min. The tailored pore size of VNU-1 resulted in size-selective properties between small-molecule antibiotics and big-molecule humic acid, and VNU-1 maintained high photodegradation performance after 5 cycles. Based on the toxicity test and the scavenger test, the products after photodegradation had no toxic effect on V. fischeri bacteria, and the superoxide radical (·O2-) and holes (h+) generated from VNU-1 dominated the photodegradation reaction. These results demonstrate that VNU-1 is a promising photocatalyst and provide a new insight for developing MOF photocatalyst to remove emerging contaminants in the wastewater systems.

Introducing defect-engineering 2D layered MOF nanosheets into Pebax matrix for CO2/CH4 separation

The layered Ni-MOF nanosheets (Ni-NS) with defective structure were used as fillers to prepare mixed matrix membranes (MMMs) for CO2 separation. In this work, the defect structure of Ni-MOF nanosheets was manipulated by adjusting the molar ratio of metal source to organic linker (RM/L), and the influence of defects at the Ni-MOF nanocrystal on the gas separation performance of MMMs was investigated. The characterization of filler and membranes showed that Ni-MOF nanosheets with defective structure could improve the gas separation performance mainly through the enlarged pore size and the increased adsorption sites. Compared with the Ni-NS-2 with complete crystal structure, the Ni-NS-8 with defective structure showed better interfacial compatibility with poly(ether-block-amide) (Pebax® MH 1657) matrix. The Pebax/Ni-NS-8-6 MMM showed the best CO2/CH4 separation performance. The CO2 permeability and CO2/CH4 selectivity were 436.1 Barrer and 33.1, which were 115% and 18% higher than those of pure Pebax membrane, respectively. The results showed that defect-engineering in MOF nanocrystals was an important strategy to optimize the gas separation performance of 2D MOF-based MMMs.

Separation Mechanisms and Anti-Fouling Properties of a Microporous Polyvinylidene Fluoride-Polyacrylic Acid-Graphene Oxide (PVDF-PAA-GO) Composite Membrane with Salt and Protein Solutions.

This research demonstrates the preparation of composite membranes containing graphene oxide (GO) and investigates the separation mechanisms of various salts and bovine serum albumin (BSA) solutions. A microporous polyvinylidene fluoride-polyacrylic acid-GO (PVDF-PAA-GO) separation layer was fabricated on non-woven support. The GO-incorporating composite resulted in enlarged pore size (0.16 μm) compared with the control membrane (0.12 μm). The zeta potential of the GO composite was reduced to -31 from -19 mV. The resulting membranes with and without GO were examined for water permeability and rejection efficiency with single salt and BSA solutions. Using the non-woven/PVDF-PAA composite, the permeance values were 88-190 kg/m2hMPa, and the salt rejection coefficients were 9-28% for Na2SO4, MgCl2, MgSO4, and NaCl solutions. These salt removals were based on the Donnan exclusion mechanism considering the ion radii and membrane pore size. Incorporating GO into the separation layer exhibited limited impacts on the filtration of salt solutions, but significantly reduced BSA membrane adhesion and increased permeance. The negatively charged protein reached almost complete removal (98.4%) from the highly negatively charged GO-containing membrane. The GO additive improved the anti-fouling property of the composite membrane and enhanced BSA separation from the salt solution.

L-Tartaric acid tailored polyamide thin-film composite membrane with enhanced performance for salt and molecular removal

High performance polyamide (PA) thin-film composite (TFC) membranes are in great demand. However, it is still a challenge to further enable PA TFC membranes to overcome the perm-selectivity tradeoff. Here, l-tartaric acid (LTA) and piperazine were first used as the aqueous phase monomers to fabricate LTA integrated PA (LTA/PA) TFC membranes via interfacial polymerization (IP) with trimesoyl chloride. The physicochemical property and separation performance of the PA TFC membranes were regulated via LTA concentrations. The introduction of LTA made the PA layer of the membrane thinner and smoother with enlarged pore size. The LTA/PA TFC membrane prepared with a higher LTA content had a maximal water flux (207.6 LMH/bar, 20 times higher than that of the control membrane), with superior rejections for the dyes (>98.0 %) and low removal rates for the salts (<4.5 %). Of note, the water flux of the membrane prepared with a low LTA content was enhanced to 18.9 LMH/bar without sacrificing the rejection of Na2SO4 (RNa2SO4 > 98.0 %). The membranes with optimal LTA content break the tradeoff towards some dyes or salts, and presented superior performance compared with most other reported polymeric membranes. This work highlights the great potential of constructing natural acid-modulated PA composite membranes in water purification.

The textural properties of cooked convenience rice upon repeated freeze–thaw treatments are largely affected by water mobility at grain level

Brown rice (BR) is a promising source for convenience rice that are mostly stored frozen. However, freezing and thawing may cause deterioration in rice texture quality. To investigate how rice texture is influenced by freeze–thaw cycles, BR, the pretreated BR with partially ruptured bran layer (UER) and white rice (WR) were cooked and treated with repeated freeze–thaw cycles, with their textural properties, variations in moisture distribution and starch structure being measured. Results showed that the repeated freeze–thaw treatment induced a progressive reduction in hardness and stickiness of all cooked rice. The reduced hardness of rice could be explained by the enlarged pore size of starch inside rice under scanning electron microscopy. Moisture migration in WR was the fastest responding to multiply freeze–thaw cycles, followed by UER, while water mobility in BR was slowest. Moreover, WR, BR and UER resulted in a similar extent of amylopectin retrogradation and chains length distribution after repeated freeze–thaw cycles. It indicated similar and minor effect of starch variations on determining the texture of different rice samples against freeze-thawing. Water mobility tended to be a main factor leading to the textural difference of fully gelatinized rice samples. This study focused on the relationship between water distribution and starch retrogradation, providing a better understanding on influences of multiple freeze-thawing on textural quality of cooked rice maintaining different extents of surface layer.

Inositol hexaphosphate assisted polyamide thin-film composite membrane with ultrahigh performance for water desalination and dye fraction

Developing membranes with highly permeable and selective separation remains a challenge. Here, inositol hexaphosphate (IP6) was first introduced into the active layer for preparing an IP6 integrated polyamide (IP6PA) thin-film composite (TFC) membrane. The IP6PA TFC membrane possessed a thinner PA layer with a smoother and better hydrophilic surface as well as strengthened electronegativity and enlarged pore size. The IP6PA membrane that was prepared with a low IP6 content presented a high pure water flux of 20.5 LMH/bar (1.6 times higher than that of the control membrane), and a high Na2SO4 rejection rate (98.5 %), which could be used to completely remove typical dyes and natural organic matters. Notably, the IP6PA membrane fabricated with a high weight ratio of IP6 exhibited an ultrahigh water flux (111.7 LMH/bar) while maintaining superior rejections for Congo red (98.5 %), Direct red 23 (98.6 %), and Brilliant blue R250 (99.5 %). The results show that the modified membrane presented excellent performance in separation of organic/salts, particularly with its outstanding permeability and superior rejection rate, compared with those of most reported polymeric membranes. This work provides a new scheme for the rational design and manufacture of natural acid regulated polyamide composite membranes with enhanced performance for water treatment.

Metal-Induced Aminosilica Rigidity Improves Highly Permeable Microporous Membranes via Different Types of Pendant Precursors.

In this study, nickel-doped aminosilica membranes containing pendant groups were prepared with 3-aminopropyltriethoxysilane (APTES), trimethoxy[3-(methylamino)propyl]silane (MAPTS), 3 N,N-dimethyl aminopropyltrimethoxysilane (DAPTMS), N-[3-(trimethoxysilylpropyl]ethylene diamine (TMSPED), and 1-[3-(trimethoxysilyl)propyl] urea (TMSPU). Differences in the structures of terminal amine ligands significantly contributed to the formation of a coordinated structural assembly. Ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and N2 adsorption isotherms revealed that short and rigid pendant amino groups successfully coordinated with nickel to produce subnanopores in the membranes, while an ion-exchange interaction was suggested for longer and sterically hindered aminosilica precursors. Moreover, the basicity of amine precursors affected the affinity of ligands for the development of a coordinated network. A pristine aminosilica membrane showed low levels of H2 permeance that range from 0.1 to 0.5 × 10-6 mol m-2 s-1 Pa-1 with a H2/N2 permeance ratio that ranges from 15 to 100. On the contrary, nickel coordination increased the H2 permeance to 0.1-3.0 × 10-6 mol m-2 s-1 Pa-1 with H2/N2 permeance ratios that range from 10 to 68, which indicates the formation of a microporous structure and enlargement of pore sizes. The strong level of coordination affinity between nickel ions and amine groups induced rearrangement of the flexible pendant chain into a more rigid structure.

Chitosan/silk fibroin biomimic scaffolds reinforced by cellulose acetate nanofibers for smooth muscle tissue engineering

Reconstruction of multilayered and functional smooth muscle tissues remains a challenge nowadays. Cryogels possess great advantages in three-dimensional tissue regeneration owing to the interconnected macroporous structure, but their applications have been hindered because of limited mechanical properties. Inspired by the natural extracellular matrix, cellulose acetate electrospun nanofibers (NFs) were incorporated to chitosan/silk fibroin (CS/SF) cryogel scaffolds to address this problem in this work. Compared with pure CS/SF scaffolds, CS/SF/NFs composite scaffolds showed roughened surface and enlarged pore size (216.2 ± 65.3 μm vs. 263.1 ± 75.7 μm) allowing for cell adhesion and proliferation. Incorporation of nanofibers upgraded the mechanical properties of scaffolds with a six-fold increase in compressive modulus. The proliferation and infiltration of smooth muscle cells (SMCs) were remarkably improved with the existence of nanofibers. Besides, SMCs cultured on CS/SF/NFs scaffolds displayed higher expression of contraction-related genes, verifying their potential for smooth muscle tissue engineering.

Preparation of nanocomposite aromatic polyamide reverse osmosis membranes by in-situ polymerization of bis(triethoxysilyl)ethane (BTESE)

Bis(triethoxysilyl)ethane (BTESE) nanoparticles were incorporated into aromatic polyamide (PA) membranes via in-situ polymerization to prepare BTESE nanocomposite PA (BTESE-TFN) membranes for reverse osmosis. In-situ polymerization was utilized to produce BTESE nanoparticles with high dispersion in PA membranes by adding BTESE as precursors into PA membranes for in-situ polymerization. Organic bridged -C-C- in BTESE provided enhanced compatibility between BTESE nanoparticles and PA membranes. The BTESE-TFN membranes showed durability with stable RO performance for more than 96 h because of the high dispersion of BTESE nanoparticles and enhanced compatibility between BTESE nanoparticles and PA membranes. The BTESE nanoparticles increased surface roughness, thickness, hydrophilicity of PA membranes. The BTESE nanoparticles changed surfaces of PA membranes to looser structure with more pores and gaps. However, low loadings of BTESE nanoparticles in the BTESE-TFN membranes were observed due to low reactivity of Si-OC2H5 groups in BTESE. Even so, salt rejection of prepared TFN-0.12 membrane was slightly improved to 96.81%, compared with that of prepared pristine PA membrane. The TFN-0.12 membrane showed water flux of 1.6 L/(m2•h•bar), 25% higher than the water flux of pristine PA membrane because of enlargement of pore sizes in BTESE nanoparticles, formation of a loose and rough membrane surface and enhancement of hydrophilicity of the membrane surface. Furthermore, modification of organic bridged groups in the BTESE exhibited great potential to further optimize the water flux and durability of BTESE-TFN membranes.

Green synthesis of MOF-808 with modulation of particle sizes and defects for efficient phosphate sequestration

In this work, a facile and green method is applied to synthesize hydrophilic MOF-808(Zr) and modulate its defect content and particle size using different amounts of iron nitrate (denoted as F) to obtain serial XF-MOF-808 (“X” implied the dosage of used F). The development of additional adsorption sites and the fine-tune of pore and particle size based on MOF-808 significantly improved phosphate adsorption performance. In particular, the 0.5F-MOF-808 shows excellent adsorption capacity (305.5 mg/g) and rapid diffusion rate (37.51 mg/g·min0.5) for phosphate at 298 K and initial pH = 6.5, outperforming pristine MOF-808 and most previously reported adsorbents. 0.5F-MOF-808 possesses a wide pH tolerance, outstanding reusability and excellent selectivity for phosphate adsorption from simulated wastewater, verified in environmental implication and regeneration experiments. Phosphate loaded on the adsorbent can be converted to struvite for agricultural fertilizer via a simple crystallization process. Compared to MOF-808, the exceptional sorption performance of 0.5F-MOF-808 is supported by decreased internal diffusion limitation, enlarged pore size and the development of new adsorption sites, which can be proved by advanced characterizations and batch adsorption experiments. This work presents a promising modification strategy of MOF materials for phosphate adsorption and recovery.

One-pot synthesis of α-Linolenic acid nanoemulsion-templated drug-loaded silica mesocomposites as efficient bactericide against drug-resistant Mycobacterium tuberculosis

Nowadays, pathogenic infection has posed a severe threat to the public health and environmental sanitation, urging a continuous search of efficacious and safe bactericidal agents of various formulated forms. Here, a facile one-pot hydrothermal preparation of mesoporous silica nanoparticles using ultrasonication-assisted nanoemulsion of α-Linolenic acid (α-LA) as template was developed. The formed silica mesocomposite at water/fatty-acid surface provides an easy yet green synthesis route, which can be generalized for the further encapsulation of hydrophobic drugs such as antimycobacterial Rifampicin (RIF). The obtained α-LA nanoemulsion-templated silica nanoparticles (LNS NPs), with a weight content of ∼17% α-LA in the composite, showed apparent antibacterial effect against Staphylococcus aureus (S. aureus). By comparison, the removal of α-LA from the silica nanoparticles (LNS-1 NPs) resulted in the composite of enlarged pore size with negligible bactericidal activities. Notably, the Isoniazide (INH) and Rifampicin (RIF)-encapsulated LNS NPs exhibited outstanding antimycobacterial activity against both drug-sensitive and drug-resistant Mycobacterium tuberculosis (M. tuberculosis). The obtained highly biocompatible, biosafe and low-energy consumptive α-LA-contained mesostructured silica-based bactericide holds promising therapeutic potentials to tackle the emerging drug-resistant infectious microbes.

Chemical Cleaning and Membrane Aging in MBR for Textile Wastewater Treatment

Membrane bioreactors have been widely used in textile wastewater treatment. Intensive chemical cleaning is indispensable in the MBR for textile wastewater treatment due to the severe membrane fouling implied. This work investigated the aging of three different membranes, polyvinylidene fluoride (PVDF), polyether sulfone (PES), and polytetrafluoroethylene (PTFE), in the MBRs for textile wastewater treatment. Pilot-scale MBRs were operated and the used membrane was characterized. Batch chemical soaking tests were conducted to elucidate the aging properties of the membranes. The results indicated that the PVDF membrane was most liable to the chemical cleaning, and the PES and PTFE membranes were rather stable. The surface hydrophobicity of the PVDF increased in the acid aging test, and the pore size and pure water flux decreased due to the elevated hydrophobic effect; alkaline oxide aging destructed the structure of the PVDF membrane, enlarged pore size, and increased pure water flux. Chemical cleaning only altered the interfacial properties (hydrophobicity and surface zeta potential) of the PES and PTFE membranes. The fluoro-substitution and the dehydrofluorination of the PVDF, chain scission of the PES molecules, and dehydrofluorination of the PTFE were observed in aging. A chemically stable and anti-aging membrane would be of great importance in the MBR for textile wastewater treatment due to the intensive chemical cleaning applied.

Chromium removal capability, water resistance and mechanical behavior of foams based on cellulose nanofibrils with citric acid

Cellulose is a natural polysaccharide with beneficial adsorbent characteristics and a correct ecologically alternative material to design new adsorbents for water remediation contaminated with pollutants, such as metal ions that are toxic and nocive against biological systems. In this contribution, we confected foams based on cellulose nanofibrils (CNFs) with citric acid, an organic tricarboxylic acid from biosources, via a freeze-drying approach. Also, we investigated the effect of citric acid content and heat finishing treatment on the activation of crosslinking reactions in the foams. The increase of citric acid content causes slight enlargement of pore size and reduction of the activation energy for the thermal decomposition of amorphous cellulose in the foams. The heat treatment significantly affects only the cellulose releasing rate in water. The mechanical behavior of the CNF foams is changed after wetting. The CNF foams presented a two-step mechanism for the chromium adsorption kinetic, involving a pseudo-second-order and intraparticle diffusion in neutral pH via reversible physisorption. Besides the metal adsorption capacity, the foams presented suitable water resistance to be applied as adsorbant in aqueous media, releasing low cellulose content via Fickian diffusion with an initial burst effect. • Cellulose foams with citric acid as green adsorbents for heavy metals. • Eco-friendly preparation of cellulose foams via freeze-drying. • Thermodynamic and kinetics for the chromium adsorption by cellulose foams. • Cellulose releasing of cellulose foams as a water resistance test. • The effect of citric acid content on cellulose foam properties.

Eco-friendly preparation of high-quality mineralized wood via thermal modification induced silica sol penetration

Application of wood as a green and sustainable material is restricted due to its easy wrapping property, deformation, biological degradation and thermal instability. Coupling thermal treatment and silica sol penetration could overcome the weakness of natural wood, and synergistically improve the overall performance. Thermal treatment showed a significant effect on hydrophobicity, hygroscopicity, surface color and compressive strength. It reduced the compressive strength to some extent due to the degradation of cell wall polymers (hemicellulose, lignin and cellulose). At above 200 ℃, the degradation of cell wall polymers, rather than hornification, was in the leading position, dominating the compressive strength. Changes in the component and structure of cell walls (chemical and physical environment) helped the penetration and deposition of silica sol owing to extra channels and enlarged pore size. Satisfied silica sol incorporation in thermally treated wood further improved the surface hydrophobicity, dimensional stability, surface hardness, and compensated the reduction on compressive strength. It was attributed to the -OH consumption (cell wall polymers degradation) and filling effect caused by silica sol networks (Si-O-Si and Si-O-C bonds) in wood. The improved thermal stability was ascribed to the coverage effect of silica sol on the inner-surfaces of wood, which could be treated as a physical barrier to prevent heat conduction. Eventually, we proposed a mechanism concerning the combination treatment for preparing silica-mineralized wood. This work opens an eco-friendly way to produce bio-based materials with high quality to be used in outdoor applications or humid environments.

Influence of solvent on aggregation of metallic Cu in Cu/MgO during hydrogenation in liquid phase

Cu/MgO catalysts generally could selectively hydrogenate C=O in unsaturated aldehydes, but they often suffer from aggregation of Cu species in liquid-phase reactions. In this study, structural change of Cu/MgO catalyst was investigated during the catalysing conversion of ethyl levulinate (EL) to γ-valerolactone (GVL) and 1,4-pentanediol (1,4-PDO) in varied medium. Water as medium could achieve GVL yield of ca. 99%, while ethanol promoted ring-opening of GVL to 1,4-PDO. However, water and ethanol impacted structure of Cu/MgO in distinct ways. Water led to transformation of MgO into Mg(OH)2, destroying interaction of metallic Cu species with MgO. This led to the increase of Cu (111) crystal planes size by ca. 300% and Cu (220) crystal planes size by ca. 200%. The use of water-ethanol as reaction medium further enhanced aggregation of Cu species. Morphology of the Cu/MgO catalyst changed to rope-like structure and abundant additional meso to large pores were created in water or ethanol-water medium. In comparison, ethanol as medium alone suppressed aggregation of metallic Cu and formation of Mg(OH)2, but re-structure of MgO by enlarging pore size also occurred. The aprotic reaction medium such as acetone, tetrahydrofuran and N,N-dimethyl formamide also affected aggregation of metallic Cu species in different ways.

Purification of high-arsenic groundwater by magnetic bimetallic MOFs coupled with PMS: Balance of catalysis and adsorption and promotion mechanism of PMS

• Efficient purification of high-arsenic groundwater by Zn/Co MOFs coupled with PMS. • Fine balance for the immobilization of As(III) by Zn/Co MOFs at Zn/Co ratio 5:1. • PMS-promoted and -accelerated elimination of both As(III) and As(V). Purification of high-arsenic (>10 µg/L) groundwater is of significance for drinking water safety all around the world. Considering the dominant presence of arsenite (As(III)) in groundwater and ineffective adsorption of As(III) by traditional adsorbents, the magnetic Zn/Co bimetallic MOFs (Zn/Co MOFs) which contain both catalytic and adsorption sites were prepared, and coupled with peroxymonosulfate (PMS) to realize the efficient simultaneous oxidation of As(III) and adsorption of evolved As(V). Considering the vital roles of oxidation and adsorption, the molar ratio of Zn and Co precursors was tuned ranging from 1: 1 to 9: 1 during Zn/Co MOFs synthesis to balance the catalysis and adsorption processes in the heterogeneous PMS system for As(III) immobilization. It was found that Zn/Co MOFs with Zn and Co molar ratio of 5: 1 possessing moderate catalytic performance and best adsorption capacity outperformed removal performance for As(III). The presence of PMS significantly promoted the elimination of both As(III) (the initial adsorption rate increased from 31.19 to 358.96 µg/g/min) and As(V) (the initial adsorption rate increased from 354.12 to 497.85 µg/g/min), which not only oxidized As(III) into As(V) by reactive species generated from PMS activation but also provided additional adsorption sites through enlarging pore size and changing chemical environment. Furthermore, Zn/Co MOFs coupled with the PMS system exhibited outstanding reusability and effectiveness for remediation of real high-arsenic groundwater.