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Graphene-based materials used in electrosorption: (1) 3D graphene; (2) graphene/MO; (3) graphene/carbon composites; (4) heteroatom-doped graphene; (5) graphene/polymer-based.

Single-atom cobalt (Co–N–C) catalyst has been proposed as a superior catalyst, but the symmetrical Co–N4 structure shows unfavorable energetics, leading to much debate on its chemical nature responsible for its high activity.

To exploit the benefits of membrane-based separation for the pharmaceutical and chemical industries, the understanding of membrane fouling in organic solvents is crucial. Specifically for the separation of biocatalysts in the manufacture of pharmaceuticals, this study investigated membrane fouling by bovine serum albumin (BSA) in 10% v/v isopropanol (IPA), 10% v/v dimethyl sulfoxide (DMSO), 30% v/v IPA, and 30% v/v DMSO, benchmarked against that in water. The presence of either IPA or DMSO worsened fouling, with the latter comparatively worse. To understand the fouling mechanisms, Field Emission Scanning Electron Microscopy (FESEM) images were taken to assess external fouling, Evapoporometry (EP) was used to measure the pore-size distributions of the fouled membranes to examine internal fouling, a fouling model was applied to extract the fouling parameters, and the interfacial interaction energies were derived. Results indicate that the worst fouling in 30% v/v DMSO was due to both significant external fouling and internal fouling, whereas the second-worst fouling by 30% v/v IPA was caused predominantly by internal fouling. The magnitudes of the total DLVO- and XDLVO-based interaction energies were found to be poorly related to the relative flux declines. This study provides valuable insights into membrane fouling in different solvent environments. Agency for Science, Technology and Research (A*STAR) Economic Development Board (EDB) Ministry of Education (MOE) We acknowledge funding from the Singapore GSK (GlaxoSmithKline) – EDB (Economic Development Board, Singapore) Trust Fund, A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Pharma Innovation Programme Singapore (PIPS) program (A20B3a0070) and A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Individual Research Grant (IRG) program (A2083c0049), the Singapore Ministry of Education Academic Research Fund Tier 1 Grant (2019-T1-002-065; RG100/19) and the Singapore Ministry of Education Academic Research Fund Tier 2 Grant (MOEMOET2EP10120-0001).

In this study, we investigated and compared the performance (permeate flux, solute rejection and membrane fouling) of an ultrafiltration membrane and a nanofiltration membrane with water and formam...

Summary Metal-sulfide photocatalysts feature outstanding optoelectronic properties and suitable band-gap energy. Photocatalyst active sites, which are rationally designed, are very important for increasing the photocatalytic reaction rate. In this review, we classify the reactive sites of metal sulfides mainly into metal-edge sites, S-edge sites, terrace sites, and defects. We summarize recent research progress in the identification and characterization of reactive sites in metal sulfides, followed by recent synthesis methods for increasing the number of these reactive sites and adjusting their reactivity. A thorough understanding of the relationship between photocatalytic performance and reactive sites in metal sulfide is helpful for enhancing the activity and selectivity. Hence, we build different correlations between the active sites of metal sulfides and photocatalytic applications, including photocatalytic hydrogen production, CO2 reduction, pollutant decomposition, and N2 fixation. Finally, we discuss the opportunities and challenges for the development of active sites in metal sulfides in photocatalysis.

Most adsorption applications involve mixtures, yet accurate predictions of the adsorption of mixtures remain challenging, in part due to the inability to account for the interplay between adsorbate-adsorbate and adsorbate-adsorbent interactions. This study involves a comprehensive Monte Carlo simulation of the adsorption of two groups of mixtures (namely, supercritical and subcritical ones) in carbon nanopores and quantifies Henry's constants, isotherms, energetics, and density distributions in the pores. When interadsorbate interactions are negligible (e.g., in supercritical mixtures such as mixtures of nonpolar gases), adsorbates behave like ideal gases and the adsorption isotherm can be predicted with the ideal adsorbed solution theory (IAST). However, when interadsorbate interactions become significant, IAST fails. This study reveals that (1) in mixtures of polar and nonpolar gases, the stronger intermolecular interaction for the polar constituent leads to synergistic adsorption that causes the nonpolar adsorbate to desorb and (2) for mixtures of polar gases, such as ethanol and water, the adsorbate-adsorbate interactions are so dominant that the unfavorable adsorbate-adsorbent interactions are overcome, such that water adsorbs onto the hydrophobic adsorbent. The competitive and synergistic interactions highlighted here are expected to be valuable in enhancing gas separations. Agency for Science, Technology and Research (A*STAR) Economic Development Board (EDB) Ministry of Education (MOE) We acknowledge funding from the Singapore GSK (GlaxoSmithKline) -- EDB (Economic Development Board, Singapore) Trust Fund, A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Individual Research Grant (IME) program (A2083c0049), the Singapore Ministry of Education Tier 1 Grant (2019-T1-002-065; RG100/19), and the Singapore Ministry of Education Tier 2 Grant (MOEMOET2EP10120-0001).

This study focusses on the hopper discharge characteristics of lognormal particle size distributions (PSDs) of non-spherical particles (namely, ellipsoids, cylinders and cuboids). Discrete element method is employed to understand the coupled effects of sphericity and lognormal PSD width. The results reveal that: (i) the ellipsoids have the most similar discharge behaviors with the spheres, but the differences increase as the PSD width increases; (ii) the packing density in the hopper increases as PSD width increases and particle sphericity decreases; (iii) regardless of sphericity, the discharge rate decreases and the jamming probability increases as the PSD width increases; (iv) for the same PSD width, the jamming probability is the greatest for cuboids and least for the ellipsoids; and (v) the lower-sphericity cylinder and cuboid have some residual particles left in the hopper upon complete discharge, and the number of residues is greater and increases with PSD width for the latter. The results provide new insights regarding the behavior of wide PSDs of non-spherical particles in the hopper, highlighting the non-negligible impact of the coupled effect of PSD and particle non-sphericity. National Research Foundation (NRF) The authors would like to acknowledge the financial support provided by the National Research Foundation (NRF), Prime Minister’s Office, Singapore, under its Campus for Research Excellence and Technological Enterprise (CREATE) program, and also the 2nd Intra-CREATE Seed Collaboration Grant (NRF2017-ITS002-013).

Pneumatic conveying experiments involving monodisperse and binary-size mixtures of glass beads with charges in the range of −10 to 10 nC have been carried out. The mass loss method was adopted, with the minimum pickup velocity (Upu) determined as the minimum velocity at which entrainment occurred. Similar to previous studies on minimum fluidization velocity, the Upu increased with particle initial charge for the positively charged particles (0–10 nC). Surprisingly, however, negatively charged particles exhibited an opposite trend such that the Upu decreased with charge magnitude. Therefore, for the particle initial charge range investigated (−10 to 10 nC), Upu increased monotonically with particle initial charge, and the correlations available (Kalman et al., 2005; Tay et al., 2012) mis-predicted Upu by up to 10 % for monodisperse systems and up to 40 % of binary-size systems. This underscores the necessity to account for particle initial charge in such correlations, particularly for polydisperse particle systems. National Research Foundation (NRF) The authors thank the financial support from the National Research Foundation(NRF), Prime Minister’s Office, Singapore, under its Campus for Research Excellence and Technological Enterprise (CREATE) program, and also the 2nd Intra-CREATE Seed Collaboration Grant (NRF2017-ITS002-013)

Sulfur dioxide (SO2) in flue gases emitted from fossil fuel power plants dramatically reduces the CO2 capture efficiency via adsorption, which is due to the potential reaction of SO2 with basic functional groups on the adsorbent. Physisorption rather than chemisorption is preferred, because adsorbents can be more easily regenerated by either reducing the pressure or increasing the temperature. Carbon is a suitable adsorbent for SO2 capture and widely used, and therefore it is important to study SO2 adsorption onto carbon with the Monte Carlo simulation to provide microscopic details to demarcate the roles of the basal plane of the graphene layer and the functional groups in adsorption. SO2 is a polar molecule like water, as they both carry partial charges, but they interact differently with functional groups. Instead of 3D-clusters in the case of water, SO2 is localized around the functional groups and spreads over the basal plane to form 2D-molecular layers because of the strong dispersive interactions with graphite. The results indicate that the functional group has a negligible effect on the enhancement of adsorption and its role is to localize 2D-clusters of SO2 molecules. For non-graphitized carbon, we have found that the greater loadings at low pressure compared to the highly graphitized carbon is due to the presence of defects (crevices) on the basal plane surface. Finally, to describe better the experimental data, we have found that the reduction in the interactions between adsorbed molecules in the first layer is because of the repulsion of their dipoles pointing normal to the surface, a phenomenon called surface mediation and is widely used in the description of gas adsorption on surfaces. Economic Development Board (EDB) Ministry of Education (MOE) We acknowledge funding from the Singapore GSK (GlaxoSmithKline) – EDB (Economic Development Board) Trust Fund and Singapore Ministry of Education Tier 1 Grant (2019-T1-002-065).

Membrane-based chiral separation has emerged as a promising method for the efficient separation of chiral molecules. Ideally, the membranes should be able to achieve good enantioselectivity, while maintaining high stability in harsh solvents. However, engineering membranes for chiral molecular separation in harsh organic solvent environments is still a big challenge. In this study, we fabricated a novel thin-film composite nanofiltration membrane composed of (2-hydroxypropyl)-beta-cyclodextrin (HP-β-CD) as the chiral selector for the enantiomeric separation of racemic 1-phenylethanol chiral compounds in organic solvents. The fabricated membrane achieved 60-80% enantioselectivity of R-phenylethanol over S-phenylethanol in nonpolar n-hexane. It was found that HP-β-CD played a critical role in the enantioselective performance, as the membrane without HP-β-CD showed no chiral selectivity. Molecular docking calculations substantiate the experiments by showing that the average free binding energy of S-phenylethanol with HP-β-CD is stronger than that of R-phenylethanol, indicating that the complex of S-phenylethanol with HP-β-CD has a higher thermodynamic stability and greater interaction. Furthermore, the crosslinked network between HP-β-CD and the polyamide layer conferred the membrane with solvent stability in nonpolar solvents. Moreover, this new membrane exhibited good solvent permeance and a molecular weight cutoff of around 650 g mol-1. Agency for Science, Technology and Research (A*STAR) Economic Development Board (EDB) Ministry of Education (MOE) Submitted/Accepted version We acknowledge funding from the Singapore GSK (GlaxoSmithKline)-EDB (Economic Development Board) Trust Fund, A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Pharma Innovation Programme Singapore (PIPS) program (A20B3a0070), A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Individual Research Grant (IRG) program (A2083c0049), the Singapore Ministry of Education Academic Research Fund Tier 1 Grant (2019-T1-002-065; RG100/19), and the Singapore Ministry of Education Academic Research Fund Tier 2 Grant (MOE-MOET2EP10120-0001).

Effective separation is critical in a wide range of applications. The focus here is on disease diagnosis in the healthcare industry and blood constituent separation in the medical industry, whereby lab-on-a-chip devices are generally limited by low throughput, which restricts separation on a practical scale. In this study, we conceive a novel Coriolis Effect Particles Segregator (CEPS), in which Coriolis force is harnessed as the key driving force for separation in a simple milli-fluidic straight-through channel and milliliters (rather than microliters) of fluids can be readily handled. First, Matlab simulations based on theoretical equations prove that perfect separation of 8 and 15 μm particles is possible. Then, Comsol simulations were performed to ascertain if an off-the-shelf milli-fluidic glass tube, coupled with Y-tube fittings as inlets and outlets, can be used. Finally, to provide proof-of-concept, a prototype was designed and built to demonstrate the practical feasibility of the CEPS. In contrast to theoretical calculations, separation was not as perfect, due to pressure differential at the outlets, need to further optimize the operating parameters (e.g., rotation speed, flow rates), adhesion of particles to channel wall, and vibration effects of the assembled setup. This study showcases the feasibility of scaling up the lab-on-a-chip design into a more practical-scale CEPS, providing a new platform for separations particularly of blood constituents (e.g., red blood cells, circulating tumor cells). Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Nanyang Technological University This work was supported by the Nanyang Technological University (Singapore) Ntuitive Multidisciplinary Grant (MOE/2018/MDT34), A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Pharma Innovation Programme Singapore (PIPS) program (A20B3a0070) and A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Individual Research Grant (IRG) program (A2083c0049), the Singapore Ministry of Education Academic Research Fund Tier 1 Grant (2019-T1-002- 065; RG100/19) and the Singapore Ministry of Education Academic Research Fund Tier 2 Grant (MOE-MOET2EP10120-0001).

Membrane fouling remains a tremendous obstacle in the implementation of membrane technology, which has motivated the use of a wide range of experimental techniques to study and understand fouling behavior in the past decades. However, molecular-level insights, which underlie the macroscopic phenomena observable experimentally-, remain incomplete. With the rapid advancement of computational power, molecular dynamics (MD) simulation has become increasingly popular to explore the interaction occurring at the ternary interface (i.e., foulant, membrane and solvent) by using explicit atom representations. MD studies have quantified interfacial physical properties and generated MD trajectories for direct visualization of the adsorption process. This review focuses on reported MD studies on membrane fouling and related foulantadsorption processes. The fundamentals of MD and procedures for constructing an MD system for fouling investigation are overviewed first. Subsequently, representative parameters and related insights generated from unbiased simulation are discussed. Then, biased simulations with enhanced sampling algorithms, which addresses some shortcomings of unbiased simulations and allows for quantification of the free energy landscape, are outlined. Additionally, the unique characteristics of representative foulants revealed by MD are summarized. Finally, future perspectives are proposed to enhance the value of MD as a tool for understanding and predicting membrane fouling. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) This study was supported by the A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Pharma Innovation Programme Singapore (PIPS) program (A20B3a0070) , A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Individual Research Grant (IRG) program (A2083c0049) , the Singapore Ministry of Educa- tion Academic Research Tier 1 Grant (2019-T1-002-065; RG100/19) and the Singapore Ministry of Education Academic Research Tier 2 Grant (MOE-MOET2EP10120-0001).

Random Forest (RF) and Neural Network (NN), respectively, were employed to understand and predict the critical flux (Jcrit) of oil-in-water emulsions in crossflow microfiltration. A total of 223 data sets from various studies were compiled, with nine operational parameters and one target variable of critical flux. RF indicated crossflow velocity (CFV) as the most dominant parameter in determining critical flux, outweighing surfactant and oil variations. Exceptions were found in specific cases when casein concentration was the most dominant, since the smaller sizes of casein significantly decreased Jcrit. The NN model predicted the best when all nine input parameters were integrated and the worst when CFV was the sole parameter used for model development, even though CFV was identified as the most dominant. The results here demonstrate the usefulness of machine learning tools to enhance the understanding on and prediction of critical flux without any governing equations. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) We acknowledge funding from the A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Pharma Innovation Programme Singapore (PIPS) program (A20B3a0070), A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Individual Research Grant (IRG) program (A2083c0049), the Singapore Ministry of Education Academic Research Fund Tier 1 Grant (2019- T1-002-065; RG100/19), and the Singapore Ministry of Education Academic Research Fund Tier 2 Grant (MOEMOET2EP10120-0001).

A scaled-up hollow fibre thin-film composite (TFC) module was successfully developed for organic solvent forward osmosis (OSFO) application in the pharmaceutical industry. The membrane consists of cross-linked P84 polyimide substrate with a polyamide selective layer, formed via interfacial polymerisation. The performance of the lab-scale module was compared to the scaled-up module in reverse osmosis and forward osmosis modes. The results from both tests revealed that the solvent permeability of the scaled-up module decreased while its selectivity increased slightly. This might be caused by the uneven distribution of liquids during interfacial polymerisation, leading to varied membrane performance. The scaled-up module was further tested for OSFO performance using a range of PEG-400 concentrations (0.5–2 M) in acetone and isopropanol as draw solutions. At 2 M PEG-400 concentration, the module demonstrated high isopropanol and acetone permeability of 0.63 LMH and 13.9 LMH, respectively. Moreover, the reverse solute flux of PEG-400 in acetone and isopropanol were relatively low at 0.188 g/l and 0.153 g/l, respectively. The module was further tested for OSFO application in the pharmaceutical industry by concentrating levofloxacin in acetone, using 2 M PEG-400 as draw solution. The process was able to concentrate levofloxacin from 1000 ppm to 16,000 ppm with very low reverse solute flux of 0.178 g/l. Therefore, this work presents a scalable TFC membrane for OSFO application in the pharmaceutical industry. Economic Development Board (EDB) Submitted/Accepted version The authors acknowledge Economic Development Board (EDB) of Singapore for funding the Singapore Membrane Technology Centre (SMTC), Interdisciplinary Graduate Programme, Nanyang Environment and Water Research Institute, Nanyang Technological University.

Adsorption is an attractive process for wastewater treatment, owing to its technical simplicity and ease of implementation. However, the adsorption process is often challenged by unoptimized efficiency, especially when the high-performing adsorbents are compacted into a packed bed column design. Herein, an electrospun nanofibrous porous scaffold is rationally designed to fractionate packing and reduce hydraulic resistance of a chromium benzene dicarboxylate-based metal–organic framework (MIL-101(Cr)) used as an adsorbent for the removal of anionic dyes. The MIL-101(Cr) adsorbent was in situ loaded via a spray-assisted method onto the electrospun scaffold in an alternating spray-and-spin fashion to deconstruct the packing and offer fractionated loading of the adsorbent materials. As compared to its unfractionated counterpart, well-fractionated MIL-101(Cr) exhibited an order of magnitude higher adsorption capacity over time with high dye removal towards Methyl Orange (MO), Acid Fuchsine (AF,) and Rose Bengal (RB). In a single pass filtration experiment, the PAN/MOF(50) ESNF-AS scaffold performed at 8808, 5066, and 7574 Lm−2h−1bar−1 water permeabilities at 2 psi with exceptional > 99 % dye removal for MO, AF, and RB dye, respectively. In addition, the spent MIL-101(Cr) adsorbent in the electrospun scaffold was able to be regenerated by alkaline and acid washing and showed good recyclability, suggesting the chemical and structural robustness of the scaffold design. This approach is highly versatile and can be adopted on different adsorbents to target the removal of different contaminants from wastewaters for a more sustainable future. Nanyang Technological University This work is supported by Singapore Membrane Technology Centre (SMTC), Interdisciplinary Graduate Programme, Nanyang Environment and Water Research Institute, and Nanyang Technological university for this research.

As the use of biocatalyst proliferates due to the need for chirally pure active pharmaceutical ingredients (API), the corresponding separation of biocatalyst and API is crucial. Although economic analyses of membrane-filtration applications exist, one dedicated to the ultrafiltration of biocatalysts remained amiss, which motivated the current study. The costs for different operating modes (i.e., constant-flux or constant-TMP) and stage configurations (i.e., single versus multiple stages), as well as the effects of feed flow rate, flux, transmembrane pressure (TMP), membrane area, recovery, and filtration rate, were evaluated. The results indicate that a capital expenditure of $1.35 million and an annual operating expenditure of $85.6 thousand are needed to install a new ultrafiltration unit for a yearly permeation of 0.64 billion liters. While capital cost depends heavily on membrane area, operating cost depends on TMP and fluid flow across the unit. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) This study was supported by A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Pharma Innovation Programme Singapore (PIPS) program (A20B3a0070), A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Individual Research Grant (IRG) program (A2083c0049), the Singapore Ministry of Education Academic Research Tier 1 Grant (2019-T1-002- 065; RG100/19), and the Singapore Ministry of Education Academic Research Tier 2 Grant (MOE-MOET2EP10120- 0001).

Graphene oxide (GO) has emerged as a promising membrane material for organic solvent nanofiltration. This study aims to understand the permeation behaviors of five polar organic solvents [namely, methanol, isopropyl alcohol (IPA), dimethyl sulfoxide (DMSO), acetone, and methyl tert-butyl ether (MTBE)] through negatively charged GO membranes, benchmarked against that of water. Among the solvents studied, water exhibits the highest permeation rate. Among the protic solvents (namely, water, methanol, and IPA), permeation decreases in the order of increasing molecular size and decreasing polarity. As for the aprotic solvents, acetone has the highest permeability due to the lowest viscosity and the smallest molecular size. The C atom of graphene in the GO membrane facilitates solvent flow because of weak interactions with the solvent molecules. Overall, the results exhibit that solvent permeation is governed by molecular size, viscosity, and membrane–solvent interactions. The findings from the study are expected to be valuable in the design of GO-based membranes for organic solvent nanofiltration. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) The authors acknowledge funding from A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Pharma Innovation Programme Singapore (PIPS) program (A20B3a0070) and under its Individual Research Grant (IRG) program (A2083c0049), the Singapore Ministry of Education Academic Research Fund Tier 1 Grant (2019-T1-002-065; RG100/19), and the Singapore Ministry of Education Academic Research Fund Tier 2 Grant (MOE-MOET2EP10120-0001).

To improve the energy efficiency of membrane distillation (MD), localized heating of the feed-membrane interface is advantageous relative to heating of the bulk feed. This motivated the current study, which targeted at developing a simple two-step way of fabricating Laser-Induced Graphene (LIG) Janus membrane for electrothermal membrane distillation. Specifically, the Janus membrane had an electrically conductive graphene side and a polydimethylsiloxane (PDMS) coated polyethersulfone (PES) side. The PES membrane was first coated with PDMS in limonene (a green solvent) and the active layer exposed to low-powered laser. Joule heating was carried out on the LIG surface by connecting two electrodes to the opposite ends of the LIG surface and providing power with an alternating current power supply at regular household frequency. This Janus membrane can be heated on the LIG surface while insulated from heat loss on the PDMS-coated PES surface, resulting in a marked improvement in the MD performance. Relative to pre-heated feed at the same power input, Joule heating of the Janus membranes gave a flux increase of up to 119.5%, specific heating energy decrease of up to 53.9% and single-pass heat utilization efficiency increase of up to 119.5%, while maintaining excellent material stability. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) This study was supported by A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Pharma Innovation Programme Singapore (PIPS) (A20B3a0070); A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Individual Research Grant (IRG) program (A2083c0049); the Singapore Ministry of Education Academic Research Tier 1 Grant (2019-T1-002-065; RG100/ 19) and the Singapore Ministry of Education Academic Research Tier 2 Grant (MOE-MOET2EP10120-0001).

In view of the proliferating applications involving membrane-based separation, the inevitable membrane fouling phenomenon is well-studied. However, the influence of foulant shape on membrane fouling remained incompletely understood. Therefore, the goal of this study was to investigate the fouling behaviors by three different shapes of latex particles (namely, peanut, pear and sphere) with similar mean diameters in the range of 3.5–3.8 μm. External and internal fouling were studied using polycarbonate track-etched (PCTE) membranes with nominal pore sizes of 2 and 8 μm, respectively. Flux data were taken, and fouling models, optical coherence tomography (OCT) and field-emission scanning electron microscope were employed. Regarding external membrane fouling, the sphere-shaped particles displayed the worst flux decline, which is tied to the greatest tendency to deposit on the membrane pores, as revealed by the network fouling model. As for internal fouling, the flux decline curves were more similar among the particle types. The fouling model shows the sphere-shaped particles gave the densest internal cake, which caused slightly steeper flux decline in the latter part of the filtration. Furthermore, OCT indicates that the highest fouling fractions at 7.5 μm below the membrane were exhibited for the peanut-shaped particles, which is due to the preferential vertical orientation resulting in deeper penetration. Results here highlight the non-negligible influence of foulant particle shape, which warrants further understanding and accounting for membrane fouling studies. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) We acknowledge funding from the A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Pharma Innovation Programme Singapore (PIPS) program (A20B3a0070), A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Individual Research Grant (IRG) program (A2083c0049), the Singapore Ministry of Education Academic Research Fund Tier 1 Grant (2019-T1-002-065; RG100/19) and the Singapore Ministry of Education Academic Research Fund Tier 2 Grant (MOE-MOET2EP10120-0001).

The Derjaguin-Landau-Verwey-Overbeek (DLVO) model, as well as the extended model (XDLVO), is popularly employed to quantify the interfacial interactions underlying membrane fouling. However, disagreements between membrane fouling extent and the interaction energies derived from DLVO or XDLVO models have been reported, which suggests gaps in the understanding. This study demonstrates that the DLVO approximation methods for predicting the interfacial foulant-membrane interaction are sensitive to the boundary condition assumptions (e.g., constant charge versus constant potential). In particular, while both the Poisson-Boltzmann (P–B) and linear superposition approximation (LSA) equations can quantify the electrostatics (EL) interaction energy component, the former assumes constant potential, while the latter additionally considers constant charge scenarios. The relative accuracy of these two equations were evaluated here. For dead-end filtration tests, flux decline trends, OCT analysis results and fouling model parameters were obtained. Regarding fouling of pristine PCTE membrane by latex particles of opposite charge signs, both the P–B and LSA equations contribute to predict relative fouling extents correctly. However, for the case of the BPEI-coated membrane, the P–B equation failed whereas the LSA equation gave good agreements. For cross-flow filtration tests in organic solvents, LSA also out-performed the P–B equation in providing more accurate predictions of membrane fouling. The results here highlight the shortcomings in the commonly used P–B equation and are expected to be potentially valuable in the development of better approximations for quantifying interfacial interaction energies. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) This study was supported by the A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Pharma Innovation Programme Singapore (PIPS) program (A20B3a0070), A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Individual Research Grant (IRG) program (A2083c0049), the Singapore Ministry of Education Academic Research Tier 1 Grant (2019-T1-002- 065; RG100/19) and the Singapore Ministry of Education Academic Research Tier 2 Grant (MOE-MOET2EP10120-0001).

Hydrogel composites with skin layer that allows fast and selective rejection of molecules possess high potential for numerous applications, including sample preconcentration for point-of-use detection and analysis. The stimuli-responsive hydrogels are particularly promising due to facile regenerability. However, poor adhesion of the skin layer due to swelling-degree difference during continuous swelling/deswelling of the hydrogel hinders its further development. In this work, a polyamide skin layer with strong adhesion was fabricated via gel-liquid interfacial polymerization (GLIP) of branched polyethyleneimine (PEI) with trimesoyl chloride (TMC) on a cross-linked N-isopropyl acrylamide hydrogel network containing dispersed poly sodium acrylate (PSA), while the traditional m-phenylenediamine (MPD)-TMC polyamide layer readily delaminates. We investigated the mechanistic design principle, which not only resulted in strong anchoring of the polyamide layer to the hydrogel surface but also enabled manipulation of the surface morphology, porosity, and surface charge by tailoring interfacial reaction conditions. The polyamide/hydrogel composite was able to withstand 100 cycles of swelling/deswelling without any delamination or a significant decrease in its rejection performance of the model dye, i.e., methylene blue. Regeneration can be done by deswelling the swollen beads at 60 °C, which also releases any loosely bound molecules together with absorbed water. This work provides insights into the development of a physically and chemically robust skin layer on various types of hydrogels for applications such as preconcentration, antifouling-coating, selective compound extraction, etc. Nanyang Technological University The authors would like to thank Nanyang Technological University, Singapore, for the research scholarship via the Interdisciplinary Graduate Programme.

Porous graphene represents promising electrocatalysts or substrates of composite electrocatalysts for various electrochemical reactions, and is well-established for renewable energy conversion and environmental remediation. Unfortunately, the lack of comprehensive understanding on the active sites of porous graphene hinders the further development of high-performance electrocatalysts. Herein, porous graphene was established for electrochemical filtration of wastewater, with results indicating that porous graphene exhibited excellent electrochemical activity in terms of high efficiency of oxidation or reduction of organic pollutants. It was experimentally and theoretically demonstrated that the –OH groups generated on the edge of porous graphene served as the active sites for the electrocatalytic reactions. The augmentation of –OH groups at the edges of graphene benefited the inner-sphere electron transfer of the electrocatalytic reactions, improving the electron transfer rates by nearly four times (from 0.034 s−1 to 0.135 s−1). Through providing these fundamental insights into the role of the active sites on the pores of porous graphene, this work furnishes future directives for the design of porous graphene-based electrocatalysts.

Transition-metal dichalcogenides (TMDs) represent an emerging class of materials showing promise in a variety of applications. The judicious stacking of two-dimensional (2D) TMDs has been reported ...

The potential risks of brominated flame retardants (BFRs) like tetrabromobisphenol A (TBBPA) have attracted much attention. However, the influence of TBBPA on functional microbes remains poorly understood, especially with regards to denitrification, which is closely related with the carbon and nitrogen cycles, eutrophication and greenhouse gas emission. Herein, we found that 1.0 mg/L of TBBPA significantly decreased the total nitrogen removal efficiency by 81.7%, but increased the accumulation of NO2−–N (by 81.5%) and N2O (by 172-fold). This was found to be underlie by the significant decrease in both the denitrifying capability of denitrifiers and total bacterial population. Further investigation revealed that TBBPA inhibited the pathways of glucolysis and pentose phosphate, and promoted glyoxylate bypass via regulating genes expressions of key enzymes (such as glucose-6-phosphate isomerase, pyruvate dehydrogenase, isocitrate lyase, etc.), then decreased the generation of NADH serving as electron donor for denitrification, and inhibited the denitrifying capability of denitrifiers. Moreover, insufficient NADH stimulated the accumulation of denitrifying intermediates (NO2−–N and N2O), which induced the increase of reactive nitrogen species (RNS), whose accumulation decreased proliferation and increased apoptosis of denitrifying bacteria. Finally, the decrease in the denitrifying capability of denitrifier and bacterial population resulted in negative denitrifying performance.

To comparatively assess the Evapoporometry (EP) technique vis-a-vis the Liquid-Liquid Displacement Porosimetry (LLDP) technique, the pore size distributions, mean pore diameters (davg) and porosities of five polymeric (namely, nylon, PES, PTFE, PET and PVDF) and one inorganic (namely, alumina) UF/tight MF membranes were quantified by both techniques. For all the membranes, the pore size ranges were generally narrower and the pore size distributions had distinctive peaks for the LLDP technique. For the nylon, PES and PTFE membranes, the davg values obtained from the two techniques agreed well. However, for the PET and PVDF membranes, the differences were twofold due to the higher pressure needed for the LLDP tests. Specifically, for PET, the davg value obtained via EP was half that via LLDP, because the higher pressure compacted the lower mechanical strength polymer, leading to pore closure. On the other hand, for PVDF, due to the rubber nature, the higher pressure caused the pores to be stretched, leading to larger pores. As for the alumina membrane, because of the more ideal cylindrical pores, the d4-weighting of the LLDP measurement gave a greater davg value than that of the d2-weighting of the EP measurement. Also, porosity measurements were erroneous for LLDP if the active layer cannot be precisely quantified. With respect to MWCO, while EP does not explicitly quantify this, the LLDP generally over-estimated the values, because of the errors associated with the measurement of the first (largest) pores at the lowest pressures.

Biomass gasification in a three-dimensional bubbling fluidized bed is numerically simulated via the computational fluid dynamics coupled with the discrete element method (CFD-DEM) incorporated with heat and mass transfer, and chemical reactions. The particle-scale investigation of the heterogeneous reaction rate of the biomass particles along with the essential aspects (including fluid force, collision force, dispersion) of the solid phase is presented. The results indicate that biomass particles behave with larger horizontal and vertical distance especially in the freeboard region than the sand particles. Strong backmixing of the solid material exists near the sidewall, and large fluid force on the particles appears in the lower bed. Similar trends of the particle-scale fluid force, velocity and dispersion can be observed for the biomass and sand particles, though the magnitudes are larger for the biomass. Chemical reactions result in the axial segregation of the biomass particles. Among all the heterogeneous chemical reactions, the char oxidation is fastest while the hydrogenating reaction is the slowest. Increasing the temperature, and steam-to-biomass ratio and equivalence ratio values all enhance the particle-scale behaviors of both the biomass and sand particles. Also, the temperature improves nearly all the reaction rates. The results obtained here provide essential understanding regarding the particle-scale behaviors of the biomass gasification process in the fluidized bed.

A CFD-DEM (computational fluid dynamics – discrete element method) model, with heat transfer, and homogeneous and heterogeneous chemical reactions accounted for, is implemented here to numerically study the biomass gasification in a three-dimensional bubbling fluidized bed. The results show that the biomass inlet on the right sidewall results in laterally asymmetrical profiles of important bed hydrodynamics and gas concentrations. Increasing the temperature, steam-biomass ratio and equivalence ratio all enlarge the gas voidage, fluid force, collision force and dispersion coefficient of the solid phase, but have different effects on the different homogeneous reaction rates. Vigorous horizontal and vertical solid dispersions occur in the lateral central and sidewalls of the bed, respectively. The results of the current work provide valuable insights regarding the hydrodynamics of the bubbling fluidized bed for biomass gasification, and are expected to be useful for the operation, scale-up and optimization of such systems for sustainable energy production.

About 3.93 billion tons of wastewater containing heavy metal complexes are discharged (e.g., from the electroplating industry) every year in China alone. It is challenging to appropriately treat su...

Fast pyrolysis of biomass produces bio-oil as a dominant product. However, the yield and composition of bio-oil are governed by numerous pyrolysis reactions which are difficult to understand because of the multiphase decomposition phenomena with convoluted chemistry and transport effects at millisecond time scales. In this work, thin-film pyrolysis experiments of biopolymers present in the biomass (i.e., cellulose (â¼50 μm), hemicellulose (using xylan as a model biopolymer, â¼12 μm), and lignin (â¼10 μm)) were performed over 200-550 °C, to investigate underlying thermal decomposition reactions, based on the product distribution obtained under reaction-controlled operating conditions. Experimental yields of non-condensable gases, bio-oil, and char at different operating temperatures and in the absence of transport limitations were obtained for each biopolymer. Cellulose- and xylan-derived bio-oil comprised of anhydrosugars, furans, and light oxygenates, in addition to pyrans in cellulosic bio-oil and phenols in xylan-derived bio-oil. Lignin pyrolysis bio-oil contained methoxyphenols, phenolic aldehydes/ketones, low-molecular-weight phenols, and light oxygenates. With an increase in the operating temperature, the anhydrosugars, furans (especially HMF and furfural), and pyrans of cellulosic and xylan bio-oils showed further degradation to form light oxygenates and furanic compounds. In the case of lignin, monolignols, initially formed at lower temperatures, further reacted to form low-molecular-weight phenols and light oxygenates with an increase in the operating temperature. In addition, based on the change in bio-oil yield and composition with temperatures, a reaction network/map was proposed for designing the molecular simulation studies of pyrolysis chemistry and developing detailed and accurate kinetics necessary for the bottom-up design of a pyrolysis reactor. Ministry of Education (MOE) This research is supported by the Ministry of Education, Singapore, under the Academic Research Fund (AcRF) Tier-2 grant (Grant No. T2-1-082).