Influence of l-lysine on the permeation and antifouling performance of polyamide thin film composite reverse osmosis membranes

Polyamide thin film composite (TFC) reverse osmosis (RO) membranes were prepared in this study. l-Lysine is used as a type of aqueous additive during interfacial polymerization. As a result, the pure water flux (PWF) of the resulting membranes increased by around 18% and their salt rejection improved from 98.17% to 98.40% at an optimum l-lysine dosage of 0.1 wt%. Additionally, the anti-fouling properties of the resulting membranes were enhanced. The chemical structure of the membranes was investigated using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The morphologies of the top surface and cross-section of the membranes were revealed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Furthermore, contact angle (CA) and zeta potential measurements were carried out to determine the surface properties of the membranes. The results showed that the TFC RO membrane became thinner, smoother, smaller in surface area, more hydrophilic and more negatively charged after the introduction of l-lysine. Accordingly, the reason for the enhancement in the PWF and anti-fouling properties of the TFC RO membranes with the introduction of l-lysine was analyzed. The thinner selective layer (increase in concentration gradient across the membrane) with carboxyl groups (hydrogen bond interactions) and loose structure (greater free volume and sub-nanometer pores) resulted in low hydraulic resistance to the permeability of the polyamide selective layer, which led to the enhancement in PWF. Also, the smoother and more hydrophilic top surface and the increase in negative charges in the selective layer contribute to the improvement in anti-fouling property.

Polyamide thin film composite (TFC) reverse osmosis (RO) membranes were prepared in this study.     

Superior performance of surface-treated NaX@Pebax-1657 membranes for O2/N2 separation

In this study, the performances of mixed matrix composite membranes (MMCMs) containing surface-treated NaX nanocrystals (ST-NaX-NCs) were experimentally and theoretically investigated for O₂/N₂ separation. For this purpose, the MMCMs were fabricated by the casting solution method and characterized by various analyses. The results reveal that there is a robust interaction between the polymer chains and the ST-NaX-NCs, and that the ST-NaX fillers are uniformly dispersed in the polymer matrix. The incorporation of ST-NaX-NCs alters the PEBAX polymer chain packing arrangement resulting in decreased membrane transport behavior for both O₂ and N₂ gases. The MMCM containing 16.7% wt ST-NaX-NCs has drastically enhanced air separation properties, with a selectivity that is increased to 204% of that of the neat membrane. Moreover, the Lewis–Nielsen model was modified by considering non-ideal effects in mixed matrix membranes, like the clogging of filler pores and polymer chain hardening around the nanocrystals, to predict the gas permeation behavior through the MMCMs. The comparison of the experimental and model results reveals that the modified model can accurately predict the gas permeability and selectivity through the MMCMs.

In this study, the performances of mixed matrix composite membranes (MMCMs) containing surface-treated NaX nanocrystals (ST-NaX-NCs) were experimentally and theoretically investigated for O₂/N₂ separation.     

A windowed carbon nanotube membrane for CO2/CH4 gas mixture penetration separation: insights from theoretical calculation

A new class of species-permselective molecular sieves with functionalized nanowindows has been prepared by modifying the armchair single-walled carbon nanotubes (SWNTs) of a pillared graphene membrane, namely windowed carbon nanotube membrane. The mechanism and characteristics of the windowed carbon nanotube membrane for the selective separation of the CO₂/CH₄ gas mixture are comprehensively and deeply studied. Selective gas separation has a great dependence not only on the interaction of the gas adsorbing on the graphene membrane and inside the CNT channel but also with the energy barrier for the gas diffusing through the nanowindow. In all the functional nanowindows investigated, CH₄ is completely rejected by the N/F-modified nanowindows while maintaining extremely high CO₂ permeability. The CO₂ permeance of the nanowindows is as high as 10⁹ GPU. It emerged that these windowed carbon nanotube membranes are efficient species-selective molecular sieves possessing excellent CO₂/CH₄ selectivity and brilliant CO₂ capture capability.

Final snapshot of the CO₂/CH₄ gas mixture separating through the windowed carbon nanotube membrane.     

Mathematical modelling of thickness and temperature dependent physical aging to O2/N2 gas separation in polymeric membranes

Polymeric membranes are glassy materials at non-equilibrium state and inherently undergo a spontaneous evolution towards equilibrium known as physical aging. Volume relaxation characteristic during the course of aging is governed by the surrounding temperature in which the polymeric material is aged. Although there are studies to understand how polymeric materials evolve over time towards equilibrium at different operating temperatures, the theories have been developed merely in response to experimental observations and phenomenological theory at bulk glassy state without the implementation of sample size effects. Limited work has been done to characterize the physical aging process to thin polymeric films using reasonable physical parameters and mathematical models with incorporation of thermodynamics and film thickness consideration. The current work applies the Tait equation of states and thickness dependent glass transition temperature, integrated within a simple linear correlation, to model the temperature and thickness dependent physical aging. The mathematical model has been validated with experimental aging data, whereby a small deviation is observed that has been explained by intuitive reasoning pertaining to the thermodynamic parameters. The mathematical model has been further employed to study the gas transport properties of O₂ and N₂, which is anticipated to be applied in oxygen enriched combustion for generation of cleaner and higher efficiency fuel in future work.

A novel mathematical model to quantify physical aging in polymeric films with simultaneous incorporation of thermodynamics and sample size effect.     

Synthesis of nitrogen doped carbon quantum dots/magnetite nanocomposites for efficient removal of methyl blue dye pollutant from contaminated water

As a remedy for environmental pollution, a simple synthesis approach has been developed to prepare nitrogen doped carbon quantum dot/magnetite nanocomposites (Fe₃O₄@NCQDs NCs) using non-toxic and cost effective lemon juice as precursor for removal of organic dye pollutant. Fe₃O₄@NCQDs NCs were characterized by using UV-Vis spectroscopy, FTIR, XRD, FESEM, EDS, TEM, VSM and TGA/DTA. TEM results show spherical shaped Fe₃O₄@NCQDs NCs with an average particle size of 5 nm. Batch adsorption studies were done to investigate the tendency of the nanocomposites to remove representative methyl blue (MB) dye from aqueous solution. The effects of MB dye concentration, dosage of Fe₃O₄@NCQDs NC adsorbent, pH, contact time and temperature were optimized by varying one variable while all the other parameters were kept constant. The experiment showed rapid removal of MB dye within 20 minutes with an adsorption efficiency of over 90.84% under optimum conditions. The adsorption process fits the Freundlich isotherm model well with R² and n values of 0.993 and 1.842, respectively, at 298 K indicating the feasibility of the adsorption process. The adsorption process is spontaneous and involves exothermic behaviour as confirmed by thermodynamic studies. From a kinetic study, it was found that the pseudo-second order model is more suitable to describe the adsorption process than the pseudo-first order model for adsorption of MB dye onto Fe₃O₄@NCQDs NCs.

Herein, we report the green synthesis of magnetic, nitrogen doped carbon quantum dot/Fe₃O₄ NPs using aqueous lemon extract for the efficient removal of organic dye pollutants from contaminated water.     

A double fluorescent nanoprobe based on phosphorus/nitrogen co-doped carbon dots for detecting dichromate ions and dopamine

An “on–off–on” fluorescent phosphorus/nitrogen co-doped carbon dot (PNCD) probe was explored for the determination of Cr(vi) and dopamine resulting from the inner filter effect (IFE). The blue-emitting carbon dots with high quantum yields of 25.47% as well as a narrow size distribution were synthesized by a rapid, convenient route using H₃PO₄ and ethylenediamine as the precursors without any surface passivation. A wide linear region in the range of 7–70 μM with a detection limit of 0.71 μM was achieved for Cr(vi). Moreover, the proper reductants can weaken the inner filter effect to recover the PNCD fluorescence by converting Cr(vi) into Cr(iii). Therefore, the PNCDs/Cr(vi) hybrid could also be used as an “off–on” fluorescent probe for detecting dopamine (DA) with a detection limit of 0.49 μM. Consequently, the PNCDs could serve as a powerful fluorescent bi-sensor for detection of both Cr(vi) and DA in practical applications.

An “on–off–on” fluorescent phosphorus/nitrogen co-doped carbon dot (PNCD) probe was explored for the determination of Cr(vi) and dopamine resulting from the inner filter effect (IFE).     

Effect of oxygen on power frequency breakdown voltage and decomposition characteristics of the C5F10O/N2/O2 gas mixture

Sulfur hexafluoride (SF₆) is widely used in the power industry because of its excellent insulation and arc extinguishing performance; however, as the global environment is deteriorating, the need to replace SF₆ is becoming significantly critical. In recent years, C₅F₁₀O has received extensive attention as a potential alternative to SF₆. In this study, a part of N₂ in C₅F₁₀O/N₂ was replaced by O₂, and the breakdown voltages of C₅F₁₀O/N₂/O₂ at different oxygen concentrations under a slightly uneven electric field were tested. The dispersion of breakdown voltage and the discharge decomposition components of C₅F₁₀O/N₂/O₂ with different oxygen concentrations were analysed. It was found that as the oxygen concentration increased, the breakdown voltage of C₅F₁₀O/N₂/O₂ with 15 kPa C₅F₁₀O at 0.2 MPa increased, and the dispersion of the breakdown voltage became worse. When 0.5% O₂ or more O₂ was added to the C₅F₁₀O/N₂ gas mixture, the carbon precipitates on the electrode surface disappeared. As the oxygen concentration continued to increase, another characteristic component, CF₂O, could be detected, whereas C₂F₄ and C₃F₆ disappeared. It is believed that O₂ can inhibit the formation of C₂F₆, C₃F₈, C₄F₁₀, and C₃F₇H. Therefore, it is recommended to use oxygen as the second buffer gas for the engineering applications of C₅F₁₀O. Moreover, the ratio of C₅F₁₀O to O₂ is recommended to be 1 : 1.

C₅F₁₀O gas mixture is a SF₆ potential substitute with high insulation strength and is a new type of environmentally friendly insulating gas. By adding oxygen to C₅F₁₀O gas mixture, insulation strength can be improved and carbon deposition can be suppressed.     

Ag-exchanged NaY zeolite introduced polyvinyl alcohol/polyacrylic acid mixed matrix membrane for pervaporation separation of water/isopropanol mixture

Ag-exchanged NaY zeolite (Ag-NaZ) particles were prepared by ion exchange and introduced to a polyvinyl alcohol (PVA) membrane cross-linked with polyacrylic acid (PAA) for the pervaporation dehydration of an isopropanol (IPA) aqueous mixture. The Ag-exchanged NaY zeolite particles were characterized by FE-SEM, EDS, BET, and XRD studies. The prepared Ag-NaZ-loaded PVA/PAA composite membrane was characterized by FE-SEM, XRD, a swelling study, and contact angle measurements. Pervaporation characteristics were investigated in terms of Ag-NaZ concentrations within PVA/PAA membranes using diverse feed solution conditions. The preferential sorption of IPA/water mixtures for Ag-NaZ-introduced membranes were also determined by calculating the apparent activation energies of IPA and water permeation, respectively. As a result, flux and selectivity increased with the Ag-NaZ concentration to 5 wt% in the membrane. Optimum pervaporation performance was observed in a 5 wt% Ag-NaZ-incorporated membrane with a flux equal to 0.084 kg m⁻² h⁻¹ and a separation factor of 2717.9 at 40 °C from an 80 wt% IPA aqueous feed solution.

Ag-exchanged NaY zeolite (Ag-NaZ) particles were prepared by ion exchange and introduced to a polyvinyl alcohol (PVA) membrane cross-linked with polyacrylic acid (PAA) for the pervaporation dehydration of an isopropanol (IPA) aqueous mixture.     

Defective S/N co-doped carbon cloth via a one-step process for effective electroreduction of nitrogen to ammonia

The electroreduction of nitrogen (N₂) has gained increasing attention as a promising route to achieve green and sustainable ammonia (NH₃) production. However, the construction of an active and durable electrocatalyst for N₂ reduction reaction (NRR) remains a significant challenge. Herein, we, for the first time, report that S/N co-doped carbon cloth (CC) with abundant defects can serve as an efficient NRR electrocatalyst at ambient conditions. The S/N co-doped CC was prepared through a novel one-step method by using ammonium persulfate (APS) as the source of nitrogen and sulfur. The catalyst prepared at 800 °C (CC-APS 800) showed abundant defects and heteroatoms as the active and stable electrocatalytic sites for NH₃ electrosynthesis. Based on this, a sizeable NH₃ yield of 9.87 × 10⁻¹⁰ mol s⁻¹ cm⁻² and high faradaic efficiency of 8.11% were obtained in 0.05 M H₂SO₄ at −0.3 V (vs. reversible hydrogen electrode, RHE), respectively. Furthermore, the electrocatalytic mechanism on CC-APS 800 was elucidated using the electrochemical in situ Fourier transform infrared technique, and follows an associative reaction pathway. Our work would provide a new guideline for designing metal-free self-standing electrocatalysts for the NRR and other applications.

The electroreduction of nitrogen (N₂) has gained increasing attention as a promising route to achieve green and sustainable ammonia (NH₃) production.     

Influence of low Bi contents on phase transformation properties of VO2 studied in a VO2:Bi thin film library

A thin-film materials library in the system V–Bi–O was fabricated by reactive co-sputtering. The composition of Bi relative to V was determined by Rutherford backscattering spectroscopy, ranging from 0.06 to 0.84 at% along the library. The VO₂ phase M1 was detected by X-ray diffraction over the whole library, however a second phase was observed in the microstructure of films with Bi contents > 0.29 at%. The second phase was determined by electron diffraction to be BiVO₄, which suggests that the solubility limit of Bi in VO₂ is only ∼0.29 at%. For Bi contents from 0.08 to 0.29 at%, the phase transformation temperatures of VO₂:Bi increase from 74.7 to 76.4 °C by 8 K per at% Bi. With X-ray photoemission spectroscopy, the oxidation state of Bi was determined to be 3+. The V⁵⁺/V⁴⁺ ratio increases with increasing Bi content from 0.10 to 0.84 at%. The similarly increasing tendency of the V⁵⁺/V⁴⁺ ratio and T_c with Bi content suggests that although the ionic radius of Bi³⁺ is much larger than that of V⁴⁺, the charge doping effect and the resulting V⁵⁺ are more prominent in regulating the phase transformation behavior of Bi-doped VO₂.

A VO₂:Bi thin-film library was fabricated by reactive co-sputtering. The phase transformation temperature of VO₂:Bi increases from 74.7 to 76.4 °C by 8 K/at% Bi in the range of 0.08–0.29 at% suggesting an effect of charge doping from Bi³⁺.     

Photoelectrochemical performance of a spin coated TiO2 protected BiVO4-Cu2O thin film tandem cell for unassisted solar water splitting

A tandem cell consisting of a Mo-BiVO₄/TiO₂/FeOOH photoanode–Cu₂O/TiO₂/MoS₂ photocathode was prepared for unassisted solar water splitting. The protective TiO₂ layer was prepared by a cost-effective spin coating technique. The individual Mo-BiVO₄/TiO₂/FeOOH photoanode and the Cu₂O/TiO₂/MoS₂ photocathode yielded a current density of ∼0.81 mA cm⁻² at 1.23 V vs. RHE and ∼−1.88 mA cm⁻² at 0 V vs. RHE, respectively under 100 mW cm⁻² xenon lamp illumination. From the individual photoelectrochemical analysis, we identify the operating points of the tandem cell as 0.66 V vs. RHE and 0.124 mA cm⁻². The positive current density from the operating points proves the possibility of non-zero operation of the tandem cell. Finally, a two-electrode Mo-BiVO₄/TiO₂/FeOOH-Cu₂O/TiO₂/MoS₂ tandem cell was constructed and analysed for unassisted operation. The obtained unassisted current density of the tandem cell was ∼65.3 μA cm⁻² with better stability compared to the bare BiVO₄-Cu₂O tandem cell. The results prove that the spin coated TiO₂ protective layer can be a viable approach to protect the photoelectrodes from photocorrosion with better stability and enhanced photoelectrochemical (PEC) performance.

Mo-BiVO₄/TiO₂/FeOOH photoanode–Cu₂O/TiO₂/MoS₂ photocathode tandem cells with photoelectrochemical stability testing.     

Construction of a ratio fluorescence assay of 5-aminosalicylic acid based on its aggregation induced emission with blue emitting N/P-codoped carbon dots

Herein, a novel ratio fluorescence method based on N/P-doped carbon dots (NPCDs) for detecting 5-aminosalicylic acid (5-ASA) in mesalazine enteric coated tablets and blood were reported for the first time. NPCDs were successfully prepared through a simple one-step hydrothermal strategy by employing adenosine triphosphate (ATP) and p-toluidine as raw materials. NPCDs exhibit bright blue emissions with excitation/emission peaks at 340/423 nm with moderate quantum yield (20.75%). In addition, 5-ASA has a certain weak fluorescence emission peak at 487 nm. Adding 5-ASA into NPCDs significantly enhanced the fluorescence intensity, which may result from aggregation induced emission (AIE) of 5-ASA on the surface of NPCDs. Therefore, NPCDs only provide self-calibration signals, and their fluorescence remains almost unchanged when co-existing with 5-ASA. Therefore, the ratio of fluorescence at F₄₈₇/F₄₂₃ was used for detection of 5-ASA. For the fluorometric determination assay, there was a good linear relationship between F₄₈₇/F₄₂₃ and 5-ASA concentration between 0.50 and 130 μM (R² = 0.9979). The detection limit was about 0.13 μM. Therefore, this method is simple, sensitive and low cost, and will be successfully applied to the detection of 5-ASA in drugs.

Herein, a novel ratio fluorescence method based on N/P-doped carbon dots (NPCDs) for detecting 5-aminosalicylic acid (5-ASA) in mesalazine enteric coated tablets and blood were reported for the first time.     

A sensitive fluorescent sensor for the detection of trace water in organic solvents based on carbon quantum dots with yellow fluorescence

The quantitative analysis of trace water in organic solvents has always been a research hotspot, and it is still in the development stage and needs to be continuously developed. In this study, a facile and rapid approach was developed for the preparation of carbon quantum dots (CQDs) with yellow fluorescence emission and ultrahigh absolute fluorescence quantum yields (92.6%). Compared to traditional organic fluorescent molecules, the preparation of CQDs is simpler, faster and more environmentally friendly. It is found that the fluorescent properties of CQDs are excellent in organic solvents and could be quenched by trace water, which makes them a promising material used without any modification for the detection of water in organic solvents. As a result, the as-prepared CQDs were adopted as fluorescent probes for the detection of water in organic solvents (ethanol, tetrahydrofuran, and 1,4-dioxane). The limit of detection was as low as 0.01%. To the best of our knowledge, this is the first time that CQDs have been used as water sensing fluorescent probes in organic solvents. The possible mechanism for trace water detection of the as-prepared CQDs in organic solvents is attributed to the specific water–fluorophore interaction and partially to the increase in polarity of the solvent caused by an increase in water concentration.

A simple fluorescent sensor for water content based on carbon quantum dots with yellow fluorescence was first demonstrated.     

Ratiometric fluorescence assay based on carbon dots and Cu2+-catalyzed oxidation of O-phenylenediamine for the effective detection of deferasirox

The monitoring of deferasirox (DEF) has important clinical roles in patients who need iron excretion. However, analytical methods with practicability and simplicity are limited. Moreover, ratiometric fluorescence strategies based on Förster resonance energy transfer (FRET) from carbon dots (CDs) as a donor are rarely reported as a drug monitor. In this work, CDs with an appropriate emitting wavelength at 480 nm and excitation around 370 nm were prepared by hydrothermal approach and HCl post-treatment. O-Phenylenediamine (OPD) can be oxidized by Cu²⁺ to produce yellow fluorescent 2,3-diaminophenazine (oxOPD) in the system of Cu²⁺ and OPD (Cu–OPD). Correspondingly, a remarkable FRET from CDs to oxOPD in the system of CDs, Cu²⁺ and OPD (CDs–Cu–OPD) was fabricated with the quenching illustration of CDs, but emitting property of oxOPD. Attributed to the chelation ability of DEF on Cu²⁺, the inhibitory effects of DEF on the Cu²⁺-triggered oxidative capability reduced the FRET system by the decreased oxOPD. Thus, the recovered CDs at F₄₈₀ and decreased oxOPD at F₅₆₀ were found through a ratiometric mode by the addition of DEF in CDs–Cu–OPD for the DEF assay. The FRET behavior of CDs and oxOPD in CDs–Cu–OPD was proved clearly through the calculation of the association constant, binding constant, number of binding sites, and the distance between the donor and acceptor. Furthermore, this ratiometric method exhibited promising analytical performance for DEF with the application in real samples. The implementation of this work expands the application field of CDs and OPD oxidation in drug monitoring, and even other biological analyses through ratiometric strategy.

CDs with appropriate emission property interacted with Cu²⁺-catalyzed oxidation of OPD to form a ratiometric fluorescence strategy for deferasirox (DEF) detection.     

Oxygen-enriched surface modification for improving the dispersion of iron oxide on a porous carbon surface and its application as carbon molecular sieves (CMS) for CO2/CH4 separation

The separation of CO₂/CH₄ can be enhanced by impregnating porous carbon with iron oxide. Dispersion of iron oxide is one of the critical factors which supports the separation process performance. Iron oxide dispersion can be enhanced by enriching the oxygen functional groups on the carbon surface. This study investigates three distinct oxidation processes: oxidation with a 10% H₂O₂ solution, ozonation with distilled water, and ozonation with a 10% H₂O₂ solution. The research steps included the following: (i) oxidation, (ii) impregnation of iron oxide followed by calcination, (iii) material characterization, and (iv) material performance analysis. Materials were characterized using N₂ sorption analysis, X-ray diffraction analysis (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy analysis (SEM-EDX), and Fourier transform infrared analysis (FT-IR). Iron oxide was well dispersed on the carbon surface, as evidenced by the elemental mapping of materials. In addition, the oxygen functional groups increased significantly in the range of 28.6–79.7% following the oxidation process, as indicated by the elemental component using SEM-EDX analysis. The impregnation of iron oxide on oxidized carbon ozonated with distilled water (COA–Fe) obtained a maximum CO₂ uptake capacity of 3.0 mmol g⁻¹ and CO₂/CH₄ selectivity increased by up to 190% at a temperature of 30 °C and pressure of 1 atm. Furthermore, the enhancement of CO₂/CH₄ separation up to 1.45 times was the best performance achieved by COA–Fe. Thus, improving iron oxide dispersion on oxidized carbon surfaces has a potential application in CO₂/CH₄ separation.

The separation of CO₂/CH₄ can be enhanced by impregnating porous carbon with iron oxide.     

Sonochemical synthesis of Co3O4 nanoparticles deposited on GO sheets and their potential application as a nanofiller in MMMs for O2/N2 separation

In this study we report an environmentally friendly, facile and straightforward sonochemical synthetic strategy for a Co₃O₄/GO nanocomposite using N,N′-bis(salicylidene)ethylenediaminocobalt(ii) as a precursor and graphene oxide sheets as an immobilization support for Co₃O₄ nanoparticles. The synthesis was facilitated by physical and chemical effects of cavitation bubbles. The synthesized nanocomposite was thoroughly characterized for its composition and morphology using Fourier transform infrared spectroscopy (FTIR), Energy dispersive X-ray spectroscopy (EDS), Scanning electron microscopy (SEM), UV-visible, Raman and X-ray diffraction spectroscopy (XRD), etc. The results show Co₃O₄ nanoparticles of 10 nm (SD 3 nm) were prepared on well exfoliated sheets of GO. The applicability of the synthesized Co₃O₄/GO nanocomposite was optimized as a nanofiller for mixed matrix membranes (MMMs) comprised of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) and polyvinyl chloride. The affinity of the prepared MMMs was evaluated for the separation of O₂/N₂ gases by varying the concentration of nanofiller, i.e. 0.03%, 0.04%, 0.05% and 0.075% (w/v). The results display high separation performance for O₂/N₂ gases with excellent permeance (N₂ 167 GPU and O₂ 432 GPU at 1 bar) and O₂/N₂ selectivity of 2.58, when the MMMs were loaded with 0.05% (w/v) of Co₃O₄/GO nanocomposite.

Sonochemical synthesis of Co₃O₄/GO nanocomposite.     

A study on fabrication of PVDF-HFP/PTFE blend membranes with controllable and bicontinuous structure for highly effective water-in-oil emulsion separation

In this study, poly(vinylidene fluoride-co-hexafluropropylene) (PVDF-HFP)/polytetrafluoroethylene (PTFE) blend membranes for water-in-oil emulsion separation were prepared via a thermally induced phase separation (TIPS) method using dibutyl phthalate (DBP) and dioctyl phthalate (DOP) as a mixed diluent. The effects of PTFE content on the obtained membranes'' structure and properties were studied. The results showed that the surface structure of the obtained membranes without addition of PTFE particles was denser and the surface pores got smaller. The porosity, pore size and hydrophobicity obviously increased with the increase in PTFE content. However, the breaking elongation and breaking strength decreased with the increase of PTFE content. When the PTFE content was 10 wt%, the obtained membrane showed the highest separation efficiency for different kinds of water-in-oil emulsions. In addition, the antifouling performance of the obtained membranes was also studied for many times of reuse. This paper introduces an effective and facile method to prepare hydrophobic–oleophilic membranes for water-in-oil emulsion separation.

PVDF-HFP/PTFE blend membranes were prepared for the first time via TIPS method with DBP and DOP as mixed diluent and PTFE as the blending polymer. The obtained membranes could separate different water-in-oil emulsions effectively.     

In situ growth of carbon dots on TiO2 nanotube arrays for PEC enzyme biosensors with visible light response

Carbon dots (CDs) were grown in situ on secondary anodized TiO₂ nanotube arrays (TiO₂ NTAs) via a hydrothermal method. The combination of CDs and TiO₂ NTAs enhanced the photoelectrochemical performance. Morphology, structure, and elemental composition of the CDs were characterized. No simple physical adsorption was found between the CDs and TiO₂, but chemical bonds were formed. UV-vis absorption and fluorescence spectroscopy showed that the CDs could enhance the absorption of TiO₂ in the visible and near-infrared regions. Owing to their up-conversion fluorescence properties, the CDs could convert low-energy photon absorption into high-energy photons, which may be used to excite TiO₂ to produce a stronger photoelectric response. Moreover, the CDs could effectively transport electrons and accept holes, thus contributing to the effective separation of electrons and holes during photoexcitation. Finally, the PEC biosensor was prepared by immobilizing glucose oxidase (GOx) on the surface of the composite. The PEC biosensor exhibited a broad range of 0.1–18 mM with a detection limit of 0.027 mM under visible irradiation because the composite material reflected strong light absorption for visible light, good conductivity, and good biocompatibility.

Carbon dots (CDs) were grown in situ on secondary anodized TiO₂ nanotube arrays (TiO₂ NTAs) via a hydrothermal method.     

Ag3PO4 nanocrystals and g-C3N4 quantum dots decorated Ag2WO4 nanorods: ternary nanoheterostructures for photocatalytic degradation of organic contaminants in water

Visible-light-driven Ag₃PO₄/graphite-like carbon nitride/Ag₂WO₄ photocatalysts with different weight fractions of Ag₃PO₄ were synthesized. Ag₂WO₄ nanorods with a scale of 500 nm to 3 μm were prepared by using a hydrothermal reaction. Via a facile deposition–precipitation technique, graphite-like carbon nitride (g-C₃N₄) quantum dots and Ag₃PO₄ nanocrystals were then deposited onto the surface of Ag₂WO₄ nanorods sequentially. Under visible-light irradiation (λ > 420 nm), the Ag₃PO₄/g-C₃N₄/Ag₂WO₄ nanorods degraded Rh B efficiently and displayed much higher photocatalytic activity than that of pure Ag₂WO₄ and the g-C₃N₄/Ag₂WO₄ composite, and the Ag₃PO₄/g-C₃N₄/Ag₂WO₄ hybrid photocatalyst with 30 wt% of Ag₃PO₄ exhibited the highest photocatalytic activity. The quenching effects of different scavengers demonstrated that reactive h⁺ and ·O²⁻ played the major roles in Rh B degradation. It was elucidated that the excellent photocatalytic activity of Ag₃PO₄/g-C₃N₄/Ag₂WO₄ for the degradation of Rh B under visible light (λ > 420 nm) can be ascribed to the efficient separation of photogenerated electrons and holes through the Ag₃PO₄/g-C₃N₄/Ag₂WO₄ heterostructure.

The ternary heterostructured Ag₃PO₄/g-C₃N₄/Ag₂WO₄ photocatalysts were successfully synthesized. The ternary composites exhibited enhanced photocatalytic activity.     

Role of defects on TiO2/SiO2 composites for boosting photocatalytic water splitting

Defect engineering of semiconductor photocatalysts is considered as an evolving strategy to adjust their physiochemical properties and boost photoreactivity of the materials. Here, hydrogenation and UV light pre-treatment of TiO₂/SiO₂ composite with the ratio of 9 : 1 (9TiO₂/1SiO₂) were conducted to generate Ti³⁺ and non-bridging oxygen holes center (NBOHC) defects, respectively. The 9TiO₂/1SiO₂ composite exhibited much higher photocatalytic water splitting than neat TiO₂ and SiO₂ as a consequence of the electronic structure effects induced by the defect sites. Electron paramagnetic resonance (EPR) indicated that hydrogenated and UV light pre-treated of 9TiO₂/1SiO₂ boosted a higher density of Ti³⁺ and NBOHC defect which could serve to suppress photogenerated electron–hole pair recombination and act as shallow donors to trap photoexcited electron. Overall, both defect sites in 9TiO₂/1SiO₂ delivered advantageous characteristic relative to neat TiO₂ and SiO₂ with the finding clearly illustrating the value of defect engineering in enhancing photocatalytic performance.

Defect engineering of semiconductor photocatalysts is considered as an evolving strategy to adjust their physiochemical properties and boost photoreactivity of the materials.