Hybrid Photocatalytic Membrane Research Articles

Tetracycline removal from wastewater via g-C3N4 loaded RSM-CCD-optimised hybrid photocatalytic membrane reactor

In this study, a split-type photocatalytic membrane reactor (PMR), incorporating suspended graphitic carbon nitride (g-C3N4) as photocatalyst and a layered polymeric composite (using polyamide, polyethersulfone and polysulfone polymers) as a membrane was fabricated to remove tetracycline (TC) from aqueous solutions as the world's second most used and discharged antibiotic in wastewater. The photocatalyst was synthesised from melamine by ultrasonic-assisted thermal polymerisation method and, along with the membrane, was characterised using various methods, including Brunauer–Emmett–Teller analysis (BET), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), Field emission scanning electron microscopy (FESEM), and Ultraviolet–visible spectroscopy (UV–Vis). The PMR process was optimised, using Design-Expert software for tetracycline removal in terms of UV irradiation time, pH, photocatalyst loading, tetracycline concentration, and membrane separation iteration. It was revealed that a membrane-integrated reactor as a sustainable system could effectively produce clean water by simultaneous removal of tetracycline and photocatalyst from aqueous solution. The maximum removal of 94.8% was obtained at the tetracycline concentration of 22.16 ppm, pH of 9.78 with 0.56 g/L of photocatalyst in the irradiation time of 113.77 min after six times of passing membrane. The PMR system showed reasonable reusability by about a 25.8% drop in TC removal efficiency after seven cycles at optimal conditions. The outcomes demonstrate the promising performance of the proposed PMR system in tetracycline removal from water and suggest that it can be scaled as an effective approach for a sustainable supply of antibiotic-free clean water.

Design of hybrid g-C3N4/GO/MCE photocatalytic membranes with enhanced separation performance under visible-light irradiation

Photocatalytic membranes with concurrent catalytic oxidation and separating functions possess promising potentials for the degradation of organic pollutants in wastewater treatment. Herein, we designed a hybrid photocatalytic membrane (viz., g-C3N4/GO/MCE) by vacuum-filtration-assisted assembling method, consisting of graphitic carbon nitride (g-C3N4) nanosheets as a top layer, graphene oxide (GO) nanosheets as an interlayer, and commercial mixed cellulose ester (MCE) as a substrate layer. The microstructures, chemical compositions, and physicochemical properties of the designed g-C3N4/GO/MCE membranes were systematically characterized by a series of characterization techniques. Particularly, photocatalysis-filtration reactor cells were designed for the evaluation of the simultaneous separation and photocatalytic degradation performance in a single unit using both organic dyes and antibiotics as modeling pollutants in wastewater. Four parameters were adopted to represent the integrated photocatalysis-filtration performance of our designed photocatalytic membranes, including permeance (P), rejection (R’, filtration alone), removal (R, combined photocatalysis-filtration under light-irradiation), and degradation rate (D). The hybrid membranes showed superior permeance and solute removal under visible-light irradiation (300 W, λ > 420 nm), in which the permeance was 20% higher than that of no-irradiation conditions. In addition, 10 consecutive cycling tests and light-on/off cycles of the as-prepared g-C3N4/GO/MCE membrane toward RhB showed quite stable permeance in the range of 268.9 to 352.9 L h−1 m−2 bar−1, and the removal was maintained in the range of 88.4% to 95.4%, indicating excellent long-term stability. Remarkably, it also exhibited good removal performance of antibiotics (e.g., ofloxacin, norfloxacin, sulfamethoxazole, erythromycin, and roxithromycin). Accordingly, the designed hybrid g-C3N4/GO/MCE photocatalytic membranes with excellent photocatalytic activity and photocatalysis-filtration performance are promising for wastewater treatment and water purification applications.

Hybrid Composite Photocatalysts Membrane System For Industrial Water Treatment And Renewable Energy Applications

A combination between the composite photocatalyst and membrane system towards the development of hybrid process for various applications especially in water treatment and renewable energy synthesis. These hybrid processes overcome many of the difficulties that are associated with conventional methods and promote process intensification. The hybrid photocatalytic membrane process could reduce the downstream process and also degrade the toxic compound in the waste water. Effluent waste water generated from industrial and domestic process, it consists of complex organic compounds such as lignin, phenolic compounds, pectin, proteins and minerals etc. The effluent containing organic dyes and phenolic compounds releases toxic materials into aquo system poses environmental concern. The traditional effluent treatment very challenge process due to consist mixture of organic and inorganic pollutants such as lignin, resins, tannins, chlorinated phenol, waxes and heavy metals etc. Recently, many industries planning to reuse treated water for economic reasons and environmental protection.

Photocatalytic membranes: a new perspective for persistent organic pollutants removal.

The presence of conventional and emerging pollutants infiltrating into our water bodies is a course of concern as they have seriously threatened water security. Established techniques such as photocatalysis and membrane technology have proven to be promising in removing various persistent organic pollutants (POP) from wastewaters. The emergence of hybrid photocatalytic membrane which incorporates both photocatalysis and membrane technology has shown greater potential in treating POP laden wastewater based on their synergistic effects. This article provides an in-depth review on the roles of both photocatalysis and membrane technology in hybrid photocatalytic membranes for the treatment of POP containing wastewaters. A concise introduction on POP's in terms of examples, their origins and their effect on a multitude of organisms are critically reviewed. The fundamentals of photocatalytic mechanism, current directions in photocatalyst design and their employment to treat POP's are also discussed. Finally, the challenges and future direction in this field are presented.

Titanium Dioxide Incorporated Polyamide Thin Film Composite Photocatalytic Membrane for Bisphenol A Removal

Polyamide thin film composite immobilized with TiO2 is prepared using M-phenylene diamine and Trimesoyl chloride via interfacial polymerization. To determine the characteristics and performance of the membranes, effect of TiO2 loading is studied. 2 (w/v) % of MPD solution and 0.2 (w/v) % of TMC/n-hexane solution were used to prepare PA TFC membrane with different amount of TiO2 loading (0 wt. %, 0.1 wt. %, 0.2 wt. %, 0.3 wt. %, 0.4 wt. % and 0.5 wt. %).PA/TiO2 composite membranes are characterized by FESEM, EDX, FTIR and water contact angle. The properties of the membranes have improved upon TiO2 loading. With over 90% of BPA rejection exhibited by all the fabricated membranes, it is proved that the membranes especially PA/TiO2 TFC membrane with 0.4 wt. % TiO2 (with the highest rejection and degradation value of 99.9% and 14% respectively) are potentially employed as the hybrid photocatalytic membrane for BPA removal.

Novel Submerged Photocatalytic Membrane Reactor for Treatment of Olive Mill Wastewaters

A new hybrid photocatalytic membrane reactor that can easily be scaled-up was designed, assembled and used to test photocatalytic membranes developed using the sol–gel technique. Extremely high removals of total suspended solids, chemical oxygen demand, total organic carbon, phenolic and volatile compounds were obtained when the hybrid photocatalytic membrane reactor was used to treat olive mill wastewaters. The submerged photocatalytic membrane reactor proposed and the modified membranes represent a step forward towards the development of new advanced treatment technology able to cope with several water and wastewater contaminants.

Photocatalytic membrane combined with biodegradation for toluene oxidation

Photocatalytic membrane coupled to biodegradation offers potential for degrading volatile organic compounds (VOCs) in photocatalytic membrane biofilm reactor. An intimately coupled photocatalysis and biodegradation reactor was operated in continuous operation for 500 days to treat simulated waste gas containing toluene. Toluene removal efficiency obtained 99%, with the elimination capacity of 550 g m−3·h−1. Membrane photocatalysis coupled to biodegradation was created to improve toluene removal from 11 to 20%. The dominant genera were Lysinibacillus, Hydrogenophaga, Pseudomonas at 30 d, Rudaea, Dongia, Litorilinea at 230 d xyl, Tod, Tcb, Bed, Tmo, Tbu, Tou, Dmp, Cat were functional genes of toluene metabolism, as shown by16S rDNA and metagenomic sequencing. Photocatalysis destroyed part of the toluene into biodegradable intermediates that were immediately mineralized by microorganisms in biofilm, some toluene was directly degraded by toluene degrading bacterial community into carbon dioxide and water. The novel hybrid photocatalytic membrane biofilm reactor is a cost-effective and robust alternative to VOCs treatment.

Performance and fouling assessment of different membrane types in a hybrid photocatalytic membrane reactor (PMR) for palm oil mill secondary effluent (POMSE) treatment

This study attempted to treat POMSE via photocatalytic membrane reactor (PMR) using different types of commercial membranes (NF-TS 40, UF-UA 60, MF-PVDF, and MF-PES membranes). The results showed that nanofiltration membrane (NF-TS 40) demonstrated the best performance due to the greater photodegradation efficiency and less fouling propensity. The best PMR condition using NF-TS 40 membrane indicated the most effective performance with greater normalized flux (0.33) and higher removal percentage of colour (99.84%), chemical oxygen demand (COD) (99.97%), biological oxygen demand (BOD) (96.24%), and turbidity (99.89%). The severity of membrane fouling based on the membrane characterisation showed a declining trend when using NF membrane in terms of foulant layer and surface roughness. Thus, the finding from this study can be set as a benchmark of an effective polishing method to treat POMSE for water reclamation due to the mitigation of membrane fouling and better performance in producing a good quality permeate.

Photocatalytic performance of TiO2/Clinoptilolite: Comparison study in suspension and hybrid photocatalytic membrane reactor

Comparison studies in suspension and hybrid photocatalytic membrane reactor (HPMR) system was investigated by using Reactive Black 5 (RB5) as target pollutant under UVA light irradiation. To achieve this aim, hybrid TiO2/clinoptilolite (TCP) photocatalyst powder was prepared by solid-state dispersion (SSD) methods and embedded at the outer layer of dual layer hollow fiber (DLHF) membranes fabricated via single step co-spinning process. TiO2 and CP photocatalyst were also used as control samples. The samples were characterized by Scanning Electron Microscopy (SEM), Energy Dispersion of X-ray (EDX), X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) analyses. The result shows that TCP was actively functioned as photocatalyst in suspension system and 86% of RB5 photocatalytic degradation achieved within 60 min; however the additional step is required to separate the catalyst with treated water. In the HPMR system, even though the RB5 photocatalytic degradation exhibits lower efficiency however the rejection of RB5 was achieved up to 95% under UV irradiation due to the properties of photocatalytic membranes. The well dispersed of TCP at the outer layer of DLHF membrane have improved the surface affinity of DL-TCP membrane towards water, exhibit the highest pure water flux of 41.72 L/m2.h compared to DL-TiO2 membrane. In general, CP can help on improving photocatalytic activity of TiO2 in suspension, increased the RB5 removal and the permeability of DLHF membrane in HPMR system as well.

Effects of hydrophilic surface macromolecule modifier loading on PES/O-g-C3N4 hybrid photocatalytic membrane for phenol removal

HydrophiLic surface modifying macromolecules (LSMM) modified polyethersulfone (PES) based photocatalytic membranes have been successfully prepared. This hybrid photocatalytic membrane applying oxygen-doped graphitic carbon nitride (g-C3N4) as a photocatalyst was successfully fabricated via phase inversion technique in flat sheet form at ambient temperature. The potential of LSMM as membrane modifier was explored in detail under various loadings (1–5 wt%). The results show that the LSMM addition successfully increased the membrane hydrophilicity which may consequently prevent the membrane from comprehensive fouling. More appearance of g-C3N4 on the membrane surface was observed by Scanning Electron Microscopy (SEM) and Atomic Force Microscope (AFM) analyses upon the LSMM addition. However, the trend tended to decline at the loading beyond 4 wt% of LSMM. At 4 wt% of LSMM, the PES/g-C3N4 membrane successfully decreased phenol concentration up to 35.78% and rejected 14.73% of phenol. From the water flux result, the application of LSMM in water treatment application was hindered by the flux deterioration but a considerably high flux for an ultrafiltration membrane. The results indicate that the introduction of LSMM in the PES/g-C3N4 hybrid photocatalytic membrane showed the great potential of LSMM as a membrane surface modifier for photocatalytic activities and membrane separation performance.

Performance of PES/LSMM-OGCN Photocatalytic Membrane for Phenol Removal: Effect of OGCN Loading.

In designing a photocatalytic oxidation system, the immobilized photocatalyst technique becomes highly profitable due to its promising capability in treating organic pollutants such as phenols in wastewater. In this study, hydrophilic surface modifying macromolecules (LSMM) modified polyethersulfone (PES) hybrid photocatalytic membranes incorporated with oxygenated graphitic carbon nitride (OGCN) was successfully developed using phase inversion technique. The effectiveness of the hybrid photocatalytic membrane was determined under different loading of OGCN photocatalyst (0, 0.5, 1.0, 1.5, 2.0, and 2.5 wt%). The best amount of OGCN in the casting solution was 1.0 wt% as the agglomeration did not occur considering the stability of the membrane performance and morphology. The highest flux of 264 L/m2·h was achieved by PES/LSMM-OGCN1.5wt% membrane. However, the highest flux performance was not an advantage in this situation as the flux reduced the rejection value due to open pores. The membrane with the highest photocatalytic performance was obtained at 1.0 wt% of OGCN loading with 35.78% phenol degradation after 6 h. Regardless of the lower rejection value, the performance shown by the PES/LSMM-OGCN1.0wt% membrane was still competent because of the small difference of less than 1% to that of the PES/LSMM-OGCN0wt% membrane. Based on the findings, it can be concluded that the optimisation of the OGCN loading in the PES hybrid photocatalytic membrane indeed plays an important role towards enhancing the catalyst distribution, phenol degradation, and acceptable rejection above all considerations.

Preparation and characterization of hydrophilic surface modifier macromolecule modified poly (ether sulfone) photocatalytic membrane for phenol removal

A modified poly (ether sulfone) (PES) by hydrophilic surface modifying macromolecules (LSMM) incorporated with oxygenated graphitic carbon nitride (OGCN) photocatalyst (PES/OGCN-LSMM) was successfully prepared as a hybrid photocatalytic membrane. The effect of solvent evaporation time during membrane fabrication was studied by focusing on the positioning of LSMM in order to provide the desirable properties of the PES/OGCN-LSMM hybrid membrane for phenol removal performance by photocatalytic and separation. The PES/OGCN-LSMM membranes exhibited a decreased value of contact angle as the solvent evaporation time increased. The SEM images revealed a dense top layer supported by finger-like structures underneath, which was formed for the membranes at 0–4 min solvent evaporation time, while a sponge-like microvoid structure was observed at 5 min of solvent evaporation time. It is interesting to highlight that as the evaporation time increased, the pure water flux decreased as the result of compact denser membrane. Benefitting the special feature of LSMM that tends to migrate upwards upon mixing, the LSMM effectively assisted OGCN photocatalyst to the top layer of the membrane. This was revealed by SEM top surface images that more OGCN photocatalyst particles were seen distributed on the dense top layer of the membrane upon longer solvent evaporation time supported by the membrane topography analysis. It was found that the phenol reduction by rejection and photocatalytic tests was the highest at 5 min solvent evaporation time, whilst water flux was the lowest. The obtained results showed that the LSMM has indeed assisted the positioning of OGCN towards the top layer of the membrane and consequently increased the photocatalytic activity of the membrane on phenol.

Physicochemical characteristic of regenerated cellulose/N-doped TiO2 nanocomposite membrane fabricated from recycled newspaper with photocatalytic activity under UV and visible light irradiation

The use of recycled newspaper as sustainable cellulose resource for the fabrication of green organic/inorganic hybrid photocatalytic membrane via phase inversion method was highlighted in this study. The incorporation of N-doped TiO2 nanorods as a nanocomposite in regenerated cellulose membrane matrix to great extent has altered its morphological and physicochemical properties, as revealed by FESEM, AFM, FTIR, XRD, XPS, and UV–visible spectroscopy analyses. FTIR analysis suggested that there is a strong interaction between the hydroxyl groups of regenerated cellulose (RC) and the TiO2 nanorods through hydrogen bonding interactions. The UV–visible spectroscopy and XPS analysis confirmed that the highly visible light absorption capability of the prepared RC/TiO2 nanocomposite membrane is due to the existence of nitrogen as dopant in the TiO2 lattice structure. The resultant membranes showed a significant photocatalytic performance in the degradation of phenol in aqueous solution under UV and visible light irradiation, respectively. It was found that 0.5wt% of TiO2 nanorods was the best loading in the regenerated cellulose membrane (RCM) with desirable physicochemical and photocatalytic properties. This study promotes the use of RC/TiO2 nanocomposite membrane as a new and green portable photocatalyst in the field of wastewater treatment without leaving any photocatalyst in the reaction system. It is crucial to emphasize that the use of a non-toxic solvent-based system in this study provide a significant contribution towards the development of a green technology system.

Novel hybrid photocatalytic reactor-UF nanocomposite membrane system for bilge water degradation and separation

Bilge water degradation and separation via a hybrid photocatalytic membrane reactor based on a polyvinylidene fluoride (PVDF)/halloysite nanotube clay (HNTs) nanocomposite membrane has been achieved by this study.

Humic acid fouling in a submerged photocatalytic membrane reactor with binary TiO2–ZrO2 particles

The binary TiO2–ZrO2 particles were better alternative to TiO2 particles as photocatalyst to reduce humic acid fouling in photocatalytic membrane reactor. The structure of the TiO2–ZrO2 particles was strongly dependent upon the content of zirconium as an additive. A composition of 50% TiO2 with 50% ZrO2 was optimal in terms of physicochemical properties. The effect of TiO2–ZrO2 particles on the reduction of humic acid fouling was further improved by the presence of divalent cations such as calcium. Nevertheless, the stability of polymeric membranes in longer-term operation using a hybrid photocatalytic membrane reactor for water treatment applications may remain a challenge.

Asymmetric TiO2 hybrid photocatalytic ceramic membrane with porosity gradient: Effect of structure directing agent on the resulting membranes architecture and performances

Asymmetric TiO2 hybrid photocatalytic ceramic membranes with porosity gradient have been fabricated via acid-catalyzed sol–gel method. Different structure directing agents (SDAs) i.e. Pluronic P-123, Triton X-100, Tween 20 and Tween 80 were incorporated in the preparation of TiO2 sol to obtain a porous multilayered TiO2 coated on the alumina ceramic support. Six different SDA-modified membrane specimens were fabricated. Four of which were coated with the TiO2 sols prepared using only one type of SDA. The remaining two specimens were fabricated via multilayer coating of different TiO2 sols prepared using different types of SDAs. Physico-chemical and morphological properties of different TiO2 layers were thoroughly investigated. The membrane M1 which had the most porous TiO2 sub-layers showed a high pure water permeability of 155Lm−2h−1bar−1. The membrane showed a relatively high Rhodamine B (RhB) removal of 2997mgm−2 over 8h treatment duration in the batch photoreactor, second only to the Pluronic-based TiO2 membrane (specific RhB removal of 3050mgm−2). All membrane specimens exhibited good performances while operated in the flow-through photocatalytic membrane reactor. Over 91% of RhB removal capability was retained after 4 treatment cycles. All membranes also showed self-cleaning property by retaining >90% of initial flux after 4 treatment cycles. The flexibility of optimizing membrane performances by fine-tuning the porosity gradient configuration of the photocatalytic layer has also been demonstrated.

The effect of UV radiant power on the rate of polysaccharide photocatalytic mineralization

Data are reported on photocatalytic mineralization rates of sodium alginate (SA), which is representative of polysaccharides commonly encountered in surface waters and effluents requiring purification. An agitated vessel-type photocatalytic reactor was employed, with suspended TiO2 nanoparticles, to study the effect of UV-A radiant power per unit volume PR (W per L reactor fluid) for which there are insufficient data. Using initial SA concentration ∼30mg/L, mineralization rates were determined, by monitoring Total Organic Carbon (TOC) reduction, in the range of UV-A PR=2.15 to 8.57 WL−1 and TiO2 concentrations 0.5 to 1.5g/L. For this well-mixed heterogeneous photocatalytic environment, the measured fairly high polysaccharide mineralization rates were fitted to a first order kinetic expression. In the parameter range studied, the kinetic constants k (of order 10−2min−1) were linearly dependent on PR with a slope in the range ∼0.6×10−2 to ∼1.0×10−2L/(Wmin). An optimum catalyst concentration near 1g/L TiO2 was observed. The experimental techniques developed and the type of kinetic data obtained are considered useful for designing photocatalytic reactors for practical applications. Moreover, it is encouraging that the measured mineralization rates are in accord with those from a continuously operated hybrid photocatalytic membrane reactor of different geometry.

High-permeability pluronic-based TiO2 hybrid photocatalytic membrane with hierarchical porosity: Fabrication, characterizations and performances

High-permeability Pluronic-based TiO2 hybrid photocatalytic membrane with hierarchical porosity has been fabricated via acid-catalyzed sol–gel method. Pluronic P-123 of different weight percentages was added to fine-tune the pore structure of the TiO2 sol and thus the resulting TiO2 layers. PVA was used as the pore fillers and binder. The sols were dip-coated layer-by-layer onto an alumina ceramic disc to fabricate hierarchically porous TiO2/alumina membrane with different porosity gradients. Physico-chemical and morphological characteristics of the membrane were investigated. Pluronic-based TiO2 photocatalytic membrane showed photo-induced super-hydrophilicity which is important for the accessibility of organic compound to the catalytic sites. The performances of the membrane were evaluated both in the batch photoreactor and continuous flow photoreactor operated in the dead-end filtration mode. In the batch photoreactor, the membrane was able to completely degrade rhodamine B despite the mass transfer limitation. The hierarchically porous Plu A membrane (which was coated with three different TiO2 layers of different pore structures) showed a high water permeability flux of 116Lm2h−1bar−1 with the corresponding intrinsic membrane resistance of 3.1×1012m−1. Plu A membrane also possessed excellent specific RhB removal of 2700mgm−2. The as-synthesized hybrid photocatalytic membrane showed a great potential for use in water and wastewater treatment owing to its fouling-control capability, high flux performances, good photocatalytic activity, and reusability.

Photocatalytic membrane reactors for water treatment from organic pollutants

The current status of research in the field of development and application of photocatalytic membrane reactors for water treatment from organic pollutants has been analyzed. The main types of these reactors and the construction techniques and properties of catalytically active membranes were discussed. The combination of photocatalysis and the membrane methods was shown to facilitate the effective removal of different organic substances from water. The factors affecting the water purification efficiency and the prospects of using the hybrid photocatalytic membrane reactors in water treatment processes were also specified.

Direct benzene conversion to phenol in a hybrid photocatalytic membrane reactor

The one-step conversion of benzene to phenol in a photocatalytic membrane reactor (PMR) coupling simultaneous reaction and product separation by means a membrane contactor is reported. The effects of parameters such as pH of aqueous TiO 2 suspensions, initial amount of benzene and catalyst concentration were investigated in the batch tests. L–L extraction experiments and transport tests, using benzene as organic extractant, showed a phenol distribution coefficient of 2.1 and an extraction percentage of 24 ± 2%, assuring, also, a constant feed of substrate in the reactive environment. Phenol production and separation was carried out in the PMR investigating the influence of pH and catalyst concentration on the performance of the system. Despite a negligible difference on the phenol flux in the benzene phase (1.16 ± 0.11 mmol h −1 m −2), a better control of formation and extraction of oxidation intermediates at pH of 3.1 was obtained. To enhance the performance of the system, photocatalytic experiments with dissolved ions (Fe 3+, Cu 2+ and V 3+) were carried out. The results showed a positive effect in presence of iron(III) ion with a phenol flux in the organic phase almost two times greater than those measured without salts.