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Photocatalytic hydrogen evolution has attracted tremendous interest as it offers a process for generation of green hydrogen based on solar radiation. But the process is extremely complex as many factors influence photocatalytic hydrogen evolution. While novel photocatalysts such as MOFs, perovskites, conjugated polymers, carbon-based materials, quantum dots, and others face challenges such as stability and scalability, semiconductor photocatalysts and cocatalysts such as TiO 2 /Pt, Ni–CdS, CdS/ZnO, CdS/ZnS have the advantages of simplicity in synthesis, stability, and scalability. Despite decades of research, challenges such as charge separation, spectrum usage, low hydrogen generation efficiency, photocatalyst stability and scalability persist. This review discusses what has been achieved so far in the domain of photocatalytic hydrogen evolution and presents a critical analysis of challenges to be addressed in developing a robust and practical photocatalytic hydrogen generation system based on efficiency of photocatalysts and their stability and the extreme importance of efficient reactor designs. [Display omitted] • Challenges associated with photocatalytic hydrogen generation systems. • Photocatalysts, cocatalysts and their stability challenges in hydrogen evolution. • Potential of semiconductor nanostructures, plasmonic nanoparticles and QDs. • Importance of reactor designs in enhancing photocatalytic hydrogen evolution. [ABSTRACT FROM AUTHOR]

The presence of contaminants of emerging concern (CEC), such as pharmaceuticals, in water sources is one of the main concerns nowadays due to their hazardous properties causing severe effects on human health and ecosystem biodiversity. Niflumic acid (NFA) is a widely used anti-inflammatory drug, and it is known for its non-biodegradability and resistance to chemical and biological degradation processes. In this work, a 10 wt.% TiO2/PVDF–TrFE nanocomposite membrane (NCM) was prepared by the solvent casting technique, fully characterized, and implemented on an up-scaled photocatalytic membrane reactor (PMR). The photocatalytic activity of the NCM was evaluated on NFA degradation under different experimental conditions, including NFA concentration, pH of the media, irradiation time and intensity. The NCM demonstrated a remarkable photocatalytic efficiency on NFA degradation, as efficiency of 91% was achieved after 6 h under solar irradiation at neutral pH. The NCM proved effective in long-term use, with maximum efficiency losses of 7%. An artificial neural network (ANN) model was designed to model NFA’s photocatalytic degradation behavior, demonstrating a good agreement between experimental and predicted data, with an R2 of 0.98. The relative significance of each experimental condition was evaluated, and the irradiation time proved to be the most significant parameter affecting the NFA degradation efficiency. The designed ANN model provides a reliable framework l for modeling the photocatalytic activity of TiO2/PVDF-TrFE and related NCM.

The research on photocatalytic membrane reactors (PMRs) started around the year 2000 with the study of wastewater treatment by degradation reactions of recalcitrant organic pollutants, and since then the evolution of our scientific knowledge has increased significantly, broadening interest in reactions such as the synthesis of organic chemicals. In this paper, we focus on some initial problems and how they have been solved/reduced over time to improve the performance of processes in PMRs. Some know-how gained during these last two decades of research concerns decreasing/avoiding the degradation of the polymeric membranes, improving photocatalyst reuse, decreasing membrane fouling, enhancing visible light photocatalysts, and improving selectivity towards the reaction product(s) in synthesis reactions (partial oxidation and reduction). All these aspects are discussed in detail in this review. This technology seems quite mature in the case of water and wastewater treatment using submerged photocatalytic membrane reactors (SPMRs), while for applications concerning synthesis reactions, additional knowledge is required.

Photocatalysis combined with membrane technology could offer an enormous potential for power generation in a renewable and sustainable way. Herein, we describe the one-step hydrogen and oxygen evolution through a photocatalytic membrane reactor. Experimental tests were carried out by means of a two-compartment cell in which a modified Nafion membrane separated the oxygen and hydrogen evolution semi-cells, while iron ions permeating through the membrane acted as a redox mediator. Nanosized Au/TiO2 and Au/CeO2 were employed as suspended photocatalysts for hydrogen and oxygen generation, respectively. The influence of initial Fe3+ ion concentration, ranging from 5 to 20 mM, was investigated, and the best results in terms of hydrogen and oxygen evolution were registered by working with 5 mM Fe3+. The positive effect of gold on the overall water splitting was confirmed by comparing the photocatalytic results obtained with the modified/unmodified titania and ceria. Au-loading played a key role for controlling the photocatalytic activity, and the optimal percentage for hydrogen and oxygen generation was 0.25 wt%. Under irradiation with visible light, hydrogen and oxygen were produced in stoichiometric amounts. The crucial role of the couple Fe3+/Fe2+ and of the membrane on the performance of the overall photocatalytic system was found. [ABSTRACT FROM AUTHOR]

Though having been studied for more than four decades, photocatalysis is still hardly applied in large-scale water and wastewater treatment. This is mainly due to the low energy efficiency of conventional photocatalytic reactors. A recently introduced reactor concept, the fixed-bed photocatalytic membrane reactor (FPMR), can potentially overcome this shortcoming. Its performance for the degradation of organic compounds is examined for different modes of operation. For this purpose, FPMRs based on commercial submerged ceramic membranes were used, which are covered by a photocatalytic layer of pyrogenic titania. The FPMRs were performed in two operational modes: closed-loop reactor and continuous-flow reactor. Oxalic acid was used as a model organic compound to conduct photocatalysis. The influence of light intensity and catalyst layer thickness as well as mass transfer inside the layer were thoroughly studied. The evaluation of the reactors was based on the apparent quantum yield, the photocatalytic space–time yield and specific energy consumption. The results demonstrate that the FPMRs are considerably more efficient than other reported reactor concepts. Its apparent quantum yield can reach up to 11.1%. Furthermore, its specific light energy consumption is merely around 0.1 kWh/g (TOC). The results also reveal that closed-loop FPMRs achieve higher efficiencies than continuous-flow FPMRs. Last but not least, a quantitative model for calculating the reaction rate constant of a photocatalytic membrane from observed reaction rate constant of a photocatalytic membrane reactor was developed and experimentally verified. [ABSTRACT FROM AUTHOR]

Photocatalytic organic synthesis/conversions and water treatment under visible light are a challenging task to use renewable energy in chemical transformations. In this review a brief overview on the mainly employed visible light photocatalysts and a discussion on the problems and advantages of Vis-light versus UV-light irradiation is reported. Visible light photocatalysts in the photocatalytic conversion of CO2, conversion of acetophenone to phenylethanol, hydrogenation of nitro compounds, oxidation of cyclohexane, synthesis of vanillin and phenol, as well as hydrogen production and water treatment are discussed. Some applications of these photocatalysts in photocatalytic membrane reactors (PMRs) for carrying out organic synthesis, conversion and/or degradation of organic pollutants are reported. The described cases show that PMRs represent a promising green technology that could shift on applications of industrial interest using visible light (from Sun) active photocatalysts.

The objectives of the current study are to assess and compare the performance of a developed photocatalytic membrane reactor (PMR) in treating industrial waste (e.g., organic dye waste) against membrane distillation. The current PMR is composed of a feed tank, which is a continuous stirred photocatalytic reactor containing slurry Titanium dioxide (TiO2) particles that are activated by using ultraviolet lamp irradiation at a wavelength of 365 nm, and a poly-vinylidene flouride (PVDF) membrane cell. The experimental setup was designed in a flexible way to enable both separate and integrated investigations of the photocatalytic reactor and the membrane, separately and simultaneously. The experimental work was divided into two phases. Firstly, the PVDF membrane was fabricated and characterized to examine its morphology, surface charge, and hydrophobicity by using a scanning electron microscope, surface zeta potential, and contact angle tests, respectively. Secondly, the effects of using different concentrations of the TiO2 photocatalyst and feed (e.g., dye concentration) were examined. It is found that the PMR can achieve almost 100% dye removal and pure permeate is obtained at certain conditions. Additionally, a kinetic analysis was performed and revealed that the photocatalytic degradation of dye follows a pseudo-first-order reaction.

Within the Adenoviridae family, human adenovirus 40 (HAdV40) is the most UV resistant serotype. This study explores photocatalytic inactivation of the pathogenic HAdV40 by UV light with TiO 2 catalyst in the presence of dissolved organic matter. Scavenging of reactive oxygen species (ROS) by dissolved organics is significant: 9.6 mg(DOC)/L decreases [OH ] by the factor of ∼17.4 with respect to that in deionized water. Regardless of the pre-filter choice ( d pore  = 0.03 μm, 0.45 μm, or 0.8 μm), the removal of the total HAdV40 by photocatalytic UV depends linearly on UV 254 fluence, Φ 254 , indicating that water quality impacts the DNA damage via fluence attenuation only. In contrast, the removal of infectious HAdV40 depends on the nature of dissolved constituents in the sample; at low Φ 254 , for the same value of fluence photocatalytic UV disinfection is more effective when using the smallest pore size (0.03 μm) pre-filter. The differences in concentration, molecular weight, and type of organic molecules that pass through different prefilters should translate into variations in the extent of quenching. Apparently, filtration through a 0.03 μm membrane produces sufficiently pure permeate for the adenovirus to become an ROS’s target competitive with remaining organic scavengers. Combining a photocatalyst-coated microfiltration membrane ( d pore  = 0.8 μm) with UV light into a photocatalytic membrane reactor removes ∼3.0 log of infectious HAdV40 in the high throughput continuous flow process with the initial specific permeate flux of 3322 ± 266 (L m −2  h −1  bar −1 ). The results point to the potential feasibility of photocatalytic disinfection as a tertiary treatment applied to a relatively high quality effluent typical for membrane filtration plants. [ABSTRACT FROM AUTHOR]

Photocatalytic membrane reactors have been recently considered as promising reactor types for photodegradation of organic compounds. In this work, a novel reactor concept named fixed-bed photocatalytic membrane reactor (FPMR), which relies on dead-end microfiltration of the catalyst particles, is introduced and studied. A quantitative model for evaluating the influence of mass transfer rate and intrinsic reaction rate on the overall photocatalytic degradation rate is developed and experimentally validated. The results show that the mass transfer rate contributes significantly to the overall reaction rate constant of the FPMR. They further reveal that the overall mass transfer coefficient and overall reaction rate constant of the reactor are greater than 4 s −1 . Those remarkably high rates are comparable to those of new photocatalytic microreactors which are two to three orders of magnitude higher than traditional photocatalytic reactors. Hence, the new reactor concept forms a powerful approach for designing photocatalytic microreactors. [ABSTRACT FROM AUTHOR]

This paper presents an overview of recent reports on photocatalytic membrane reactors (PMRs) in organic synthesis as well as water and wastewater treatment. A brief introduction to slurry PMRs and the systems equipped with photocatalytic membranes (PMs) is given. The methods of PM production are also presented. Moreover, the process parameters affecting the performance of PMRs are characterized. The applications of PMRs in organic synthesis are discussed, including photocatalytic conversion of CO2, synthesis of KA oil by photocatalytic oxidation, conversion of acetophenone to phenylethanol, synthesis of vanillin and phenol, as well as hydrogen production. Furthermore, the configurations and applications of PMRs for removal of organic contaminants from model solutions, natural water and municipal or industrial wastewater are described. It was concluded that PMRs represent a promising green technology; however, before the application in industry, additional studies are still required. These should be aimed at improvement of process efficiency, mainly by development and application of visible light active photocatalysts and novel membranes resistant to the harsh conditions prevailing in these systems.

Photocatalysis combined with membrane technology could offer an enormous potential for power generation in a renewable and sustainable way. Herein, we describe the one-step hydrogen and oxygen evolution through a photocatalytic membrane reactor. Experimental tests were carried out by means of a two-compartment cell in which a modified Nafion membrane separated the oxygen and hydrogen evolution semi-cells, while iron ions permeating through the membrane acted as a redox mediator. Nanosized Au/TiO2 and Au/CeO2 were employed as suspended photocatalysts for hydrogen and oxygen generation, respectively. The influence of initial Fe3+ ion concentration, ranging from 5 to 20 mM, was investigated, and the best results in terms of hydrogen and oxygen evolution were registered by working with 5 mM Fe3+. The positive effect of gold on the overall water splitting was confirmed by comparing the photocatalytic results obtained with the modified/unmodified titania and ceria. Au-loading played a key role for controlling the photocatalytic activity, and the optimal percentage for hydrogen and oxygen generation was 0.25 wt%. Under irradiation with visible light, hydrogen and oxygen were produced in stoichiometric amounts. The crucial role of the couple Fe3+/Fe2+ and of the membrane on the performance of the overall photocatalytic system was found.

The investigations on the influence of humic acids (HAs) being representatives of Natural Organic Matter (NOM) and inorganic salts (NaHCO 3 , Na 2 HPO 4 and Na 2 SO 4 ) representing inorganic ions in natural waters, on fouling and stability of a polyethersulfone ultrafiltration membrane in a photocatalytic membrane reactor (PMR) are reported. The influence of inorganic ions on the permeate flux was dependent on their concentration and was more significant at higher salts content. The HCO 3 − ions contributed to the permeate flux decline to the highest extent, which was attributed to both a higher feed pH and a formation of a dense fouling layer. In the presence of SO 4 2 − the permeate flux was higher than in case of other ions which was explained in terms of lower thickness of the fouling cake caused by repulsion of TiO 2 particles by the membrane under such conditions. The most severe decrease of the permeate flux observed in the presence of a mixture of HAs and inorganic salts was attributed to the formation of a thick fouling cake caused by bridging effect between HAs molecules and TiO 2 particles under high ionic strength conditions. The inorganic salts contributed also to a decrease of HAs decomposition rate due to the hole and hydroxyl radicals scavenging effect of the ions. It was found that the conditions prevailing in the PMR contributed to the loss of the membrane separation properties towards dextrans due to the abrasive action of TiO 2 particles. However, the extent of the observed decrease in the dextrans rejection was dependent on the feed composition. [ABSTRACT FROM AUTHOR]

A comparison of the efficiency of treatment of surface water from Miedwie Lake (Poland) in hybrid systems coupling various advanced oxidation processes (TiO2 photocatalysis, UVC photolysis and UV/H2O2) and ultrafiltration (UF) is presented. A ceramic membrane with ZrO2 separation layer (Inside Céram, 5,000 g mol-1) was used. Application of photocatalysis contributed to the improvement of the permeate flux compared with photolysis by ca. 16%-35%. Similar effect was observed in case of UV/H2O2 process with addition of 0.15 gH2O2 L-1. Adsorption of organic contaminants on TiO2 influenced significantly on the treatment efficiency in the photocatalytic membrane reactor (PMR). The highest removal rate of total organic carbon was observed in case of 1 g TiO2 L-1. Similar efficiency of mineralization was found in UV/H2O2 -UF process with application of 0.15 gH2O2 L-1. The UV/H2O2-UF system was found to be a promising alternative for the PMR during treatment of surface water. [ABSTRACT FROM AUTHOR]

To date no information about the stability of the polymer membranes in photocatalytic membrane reactors (PMRs) has been published. In order to implement this technology into the full scale the lifespan of the membranes should be assessed. In this paper the investigations on the influence of membrane properties, type of a TiO 2 photocatalyst (P25, ST-01, A700, and A800), a presence of oxidative species and the process parameters such as feed cross flow velocity and transmembrane pressure (TMP) on the stability of commercial polyethersulfone ultrafiltration membranes with different cut-off in a PMR are presented. Under the conditions prevailing in the PMR all the tested membranes lost their separation properties towards dextrans. The membrane characterized by the finest pores and thus the most delicate skin layer was damaged to the highest extent. The small angular-shaped particles of ST-01 caused a more severe damage of the membrane surface than the large round-edge shaped particles of A800. The deterioration of the membrane separation properties was less severe at low (1 bar) TMP value compared to that at TMP of 3 bar. The loss of the separation properties of the membranes was caused to a greater extent by the abrasion of their surface by the photocatalyst particles than by the action of oxidative species. [ABSTRACT FROM AUTHOR]

Photocatalytic membrane reactors (PMRs), coupling photocatalysts and membranes in a single system, have shown a considerable potential to reduce membrane fouling, which is one of the major drawbacks of using membranes to treat water and wastewater. In this study, the visible light-activated photocatalysts were incorporated into the polyacrylonitrile (PAN) casting solution to synthesize the photocatalytic composite membranes. The physicochemical properties and the morphology of the membranes and photocatalysts were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction analysis (XRD), ultraviolet–visible diffuse reflectance spectroscopy (UV–visible DRS), photoluminescence (PL), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Brunauer-Emmett-Teller (BET), porosimetry, and contact angle analyses. The performance of the synthesized photocatalytic mixed matrix membranes (MMMs) in treating water containing humic acid, as one of the major components in natural organic matter (NOM) existing in drinking water sources, was investigated. Under visible light irradiation, the PAN/TiO 2 @MIL-88A (Fe) MMMs simultaneously adopted photocatalysis and membrane separation in the PMR and thereby enhanced humic acid removal and anti-fouling properties. The best synthesized photocatalytic membrane could remove 92.4% of the humic acid once exposed to visible light. The optimum membrane had suitable water permeability, a high flux recovery ratio (99.5%), and a 13.5% decline in the humic acid flux after a 10-h run, considerably lower compared to the corresponding decline of the pristine membrane (37.5% over the same period). The remarkable properties of the PAN/TiO 2 @MIL-88A (Fe) membrane, including its high anti-fouling specification, confirm the appropriateness of the synthesized MMM for treating water involving humic acid. [Display omitted] • A photocatalytic membrane reactor was used to remove humic acid from wastewater. • TiO 2 @MIL-88A (Fe) was incorporated into polyacrylonitrile (PAN) membrane. • Visible light irradiation improved humic acid removal by the doped membrane. • Doped membrane exhibited enhanced hydrophilicity and antifouling properties. • Doped membrane showed nearly constant humic acid flux over a 10-h run. [ABSTRACT FROM AUTHOR]

The study describes the first application of photocatalytic membranes for virus removal and inactivation. In the proposed hybrid treatment process, a UV lamp and a microfiltration membrane are positioned in foci of two parabolic reflectors facing each other and UV light is focused on a photocatalyst-coated outer surface of the microfilter. The ceramic tubular membrane (nominal pore size of 0.8 μm) is operated in an inside-out geometry. To evaluate virus removal and inactivation efficiency of the hybrid photocatalytic microfiltration–UV process, bacteriophage P22 is used as a model virus. The kinetics of P22 inactivation by direct UV is found to fit Collins–Selleck model with the coefficient of specific lethality Λ CS = 1.972. Batch UV disinfection and crossflow filtration tests with membranes coated or uncoated with a layer of photocatalyst show that the hybrid photocatalytic microfiltration–UV process is considerably more effective in inactivating the virus (LRV = 5.0 ± 0.7) than the constituent processes – UV disinfection and microfiltration – applied in series (aggregate LRV = 2.0 ± 0.5) or together but without the photocatalytic coating on the membrane (LRV = 2.4 ± 0.2). Potential applications of the proposed treatment process include disinfection of turbid, high fouling potential and high flow rate streams. [ABSTRACT FROM AUTHOR]

The evaluation of the influence of photocatalyst (TiO 2 P25) loading, feed cross-flow velocity ( v ), transmembrane pressure (TMP) and feed pH on the fouling phenomenon of polyethersulfone microfiltration (HFK618 – 0.1 μm) and ultrafiltration (UE10 – 10 kDa, UE50 – 100 kDa) membranes in a photocatalytic membrane reactor (PMR) is presented. Scanning electron microscopy, atomic force microscopy and laser scanning microscopy were applied for the observation of the fouling cake. The increase of the velocity v led to an increase of the permeate flux which was attributed to the formation of a thinner TiO 2 layer. The permeate flux, the thickness and the roughness of the fouling layer depended on the TiO 2 loading only at the first stage of the process. The increase of TMP resulted in a stronger flux decline caused by the increase of the fouling layer thickness. No permeate flux deterioration was observed in case of HFK618 and UE10 when TMP of 0.05-0.1 MPa was used. In case of UE50 exhibiting the highest pure water flux the fouling was the most severe. When the feed pH was changed to pH 3 or 9 the flux decline was much stronger than when no pH adjustment was done. [ABSTRACT FROM AUTHOR]

The performance of two photocatalytic membrane reactors (PMRs), utilizing ultrafiltration (UF) -- PMR1, or direct contact membrane distillation (DCMD) - PMR2, during treatment of primary (PE) and secondary (SE) effluents of municipal wastewater treatment plant is presented. Additionally, single UF and DCMD were also examined. TiO2 Aeroxide® P25 (0.5-1.5 g/dm³) was applied as a photocatalyst. Photocatalysis contributed to an improvement of the permeate flux in PMR1 compared to UF alone for 25-38% in case of PE and for 33% when SE were used. Based on SEM, AFM and contact angle measurements the flux improvement was attributed to the porous structure of TiO2 cake and hydrophilicity of the TiO2 - covered membrane. On the opposite, no flux decline during treatment of SE in PMR2 was found. However, in case of PE a decrease of the flux for ca. 40-50%, regardless of the presence or absence of TiO2, was observed. That was due to the formed dense fouling layer, which contributed to the increase of mass and thermal resistances. Permeate quality was higher in PMR2 than in PMR1. However, since mineralization of dissolved organic carbon in feed was very low, the treatment efficiency was attributed mainly to membrane separation rather than to photocatalysis. [ABSTRACT FROM AUTHOR]

BACKGROUND The pollution of the aquatic environment by pharmaceuticals has become a serious problem. Conventional technologies applied in water or sewage treatment plants are not effective in drugs removal, therefore there is an urgent need to develop new methods. RESULTS The removal of diclofenac ( DCF), ibuprofen ( IBU) and naproxen ( NAP) sodium salts in a photocatalytic membrane reactor ( PMR) utilizing direct contact membrane distillation and UV-C radiation from ultrapure water, tap water, primary effluents ( PE) and secondary effluents ( SE) of municipal wastewater treatment plant is presented. When PE were used as feed and TiO2 loading of 0.5 g dm−3 was applied, DCF was removed completely, IBU amount decreased for 73% and NAP for 90%. In the case of SE, DCF, IBU and NAP concentrations decreased by 100%, 93% and 94%, respectively (1.5 gTiO2 dm−3). Mineralization was low and did not exceed 14% for PE and 23% for SE. No drugs were found in the distillate, however, it contained high level of N- NH4+, especially in PE. CONCLUSION The hybrid system can be an effective technology for the removal of pharmaceuticals from SE and PE, however, owing to membrane fouling the latter should be pretreated before application in the PMR. © 2014 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: A photo-catalysis and dynamic membrane reactor system (PMR), with coated nanoCaCO3 layer on polypropylene non-woven fabric material, was studied for continuous photocatalysis and retention of catalysts in a single device, in removing halogenated compounds (2,4,6-Tribromophenol and 2,4-Dichlorophenol) in water. Both the batch and the continuous photocatalytic experiments were carried out to investigate the efficiency in COD removal, in removing halogenated compounds and in dehalogenation. A comparison of the separation performance of photocatalysts between bare (uncoated) and pre-coated nanoCaCO3 dynamic membranes was conducted. The pre-coated dynamic membrane can significantly enhance the filtration performance and improve the retention of photocatalysts. Particularly, nanoCaCO3 was found able to assist and improve debromination efficiency during UV irradiated photolysis. Tentative debromination pathway and dehalogenation mechanism were proposed. Due to the assisted additional reaction by the nanoCaCO3 dynamic membrane, the PMR system with nanoCaCO3-coating and Fe-ZnIn2S4 completely removed halogenated compounds, achieved highest COD removal (72% for 2,4,6-Tribromophenol and 75% for 2,4-Dichlorophenol), 85–90% debromination and 99% dechlorination efficiencies. The long-term continuous photocatalytic debromination experiments demonstrated that the dynamic membrane hybrid system was very steady in the long-term operation and the debromination maintained at about 85% during the 40h photocatalytic debromination reaction. The combination of dynamic membrane and photocatalysis provides a new alternative for practical application of photocatalysis. [Copyright &y& Elsevier]

Abstract: A photocatalytic membrane reactor combining a visible-light BiOBr photocatalyst and direct contact membrane distillation was studied for the removal of methyl orange from an aqueous solution. The hierarchical flower-like BiOBr microspheres, assemblies of BiOBr nanosheets, exhibited high efficiency for methyl orange photo-degradation under visible-light irradiation and due to their large specific surface area, their visible-light absorbance and the lower recombination of photo-generated electrons and holes. The main active species during the photo-degradation process was determined to be radicals. The organic pollutant and catalyst were retained on the feed side, as the membrane distillation only allowed water vapor to permeate through the hydrophobic membrane, leading to a high quality water stream on the permeate side. The micrometer size of the BiOBr photocatalyst may prevent fouling of the polytetrafluoroethylene membrane, making the photocatalytic membrane reactor applicable for industrial wastewater treatment. [Copyright &y& Elsevier]

Abstract: A photo-catalysis and dynamic membrane reactor system (PMR), with coated dynamic layer on polypropylene non- woven fabric material, was studied for continuous photocatalysis and retention of catalysts in a single device, in removing halogenated compound 2,4,6-Tribromophenol in water. Different dynamic layer materials such as graphite oxide, graphene oxide and nonoCaCO3 were applied to evaluate the efficiency in removing COD, 2,4,6- Tribromophenol and in debromination. The pre-coated dynamic membrane can significantly enhance the filtration performance and improve the debromination efficiency. The PMR system with dynamic layer and Fe-ZnIn2S4 photocatalyst completely removed 2,4,6-Tribromophenol when the retention time maintained 2.0h in the continuous mode. The hybrid system achieved 58%, 74% and 85% debromination when the dynamic layer materials were graphite oxide, graphene oxide and nanoCaCO3, respectively. And, the COD removal efficiencies were in the order of nanoCaCO3 (72%) > graphite oxide (51%) > graphene oxide (42%). NanoCaCO3 was found able to assist and improve debromination efficiency during UV irradiated photolysis. The combination of dynamic membrane and photocatalysis provides a new alternative for practical application of photocatalysis. [Copyright &y& Elsevier]

Abstract: The investigations on a hybrid photocatalysis–direct contact membrane distillation system for removal of ibuprofen sodium salt (IBU) from tap water are described. A comparison of the effectiveness of photodegradation in the batch and continuous flow modes is presented. Moreover, the effect of the feed solution composition on permeate flux and membrane scaling during long term process is discussed. The influence of the operation mode on the effectiveness of IBU decomposition and mineralization was found to be not significant. However, due to continuous supply of treated water the amount of TOC in feed solution in case of the continuous mode was higher compared to the batch one. After 54h of the PMR operation the flux decline for ca. 7% compared to pure water flux was observed. After 188h of the process the flux decreased for ca. 86%. The deposit layer formed on a membrane surface was composed of a thin porous TiO2 layer on which the calcite and aragonite crystals were present. Application of cleaning with HCl solution allowed to dissolve the CaCO3 scale deposit and recover the flux. No significant influence of the operation mode on the product (distillate) quality was found. Due to more potential for full scale application the continuous operation mode was recommended. [Copyright &y& Elsevier]

Abstract: A novel photocatalytic membrane reactor (PMR) system was reported by the usage of TiO2 nanotube (TNT) photocatalysts and microfiltration (MF) membranes. TNTs were prepared by hydrothermal method and the optimal preparation conditions were determined. Results showed that prepared TNT had good photocatalytic activity which was 2.5 times higher than that of P25 in reactive brilliant blue X-BR degradation. Due to its one-dimensional structure, the membrane flux in TNT separation was also 4–5 times higher than P25 no matter what kind of membrane was applied. Surface morphology analysis predicted less membrane fouling and better recycling in TNT PMR system. [Copyright &y& Elsevier]

Abstract: The main technical barriers that impede photocatalytic membrane reactor (PMR) commercialization remain on the post-recovery of the catalyst particles after water treatment. To overcome this problem, surface modification of polypropylene macroporous membrane was performed with the technique of photoinduced reversible addition-fragmentation chain transfer grafting polymerization of acrylic acid. Titanium oxide photocatalysts were introduced to the acrylic acid grafted membrane surface. Phenol decomposition was carried out under UV irradiation in a recycle batch photocatalytic membrane reactor. The normalized membrane flux reached 1.7 times that of the unmodified membrane for the PAAc modified membrane. Introducing TiO2 photocatalysts to the membrane surface reduced the normalized membrane flux slightly. For the PMR with a grafting degree of 12.9% (wt) of PAAc on the membrane surface, the corresponding decomposition percentage was 32.5% after 6h UV light irradiation. [Copyright &y& Elsevier]

Abstract: The presented studies have focused on application of modified titanate nanotubes (TNTs) for decomposition of Acid Red 18 in water. The TNTs were prepared via hydrothermal method. The post-treatment of TNTs was carried out by calcination of the as-received nanotubes at temperatures of 400–700°C. The photocatalytic experiments revealed that the most active towards AR18 decomposition were TNTs calcinated at 600°C (TNT600). However, the photocatalytic activity of the calcinated titanate nanotubes, regardless of the annealing temperature applied was found to be lower than that of P25. In the second step of the investigations, the TNT600 were applied for degradation of AR18 in a photocatalytic membrane reactor coupling photocatalysis with membrane distillation. The effect of photocatalyst loading on the effectiveness of degradation of AR18 was especially investigated. After 5h of irradiation the amount of AR18 was lowered for ca. 67, 80 and 97% for TNT600 loadings of 0.1–0.5g/dm3, respectively. The mineralization of the organics was significantly lower than the decolorization of the solution. The amount of TOC after 5h of the experiment decreased for 20, 27 and 57%, for 0.1–0.5g TNT600/dm3, respectively. Amongst products and by-products of AR18 photodegradation organic acids (formic, acetic and oxalic) and inorganic ions (nitrite, nitrate, ammonia and sulfate) were detected. The product of the hybrid process (distillate) was high quality water with conductivity in the range of 2.3–3μS/cm. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents an overview of the hybrid photocatalysis-membrane processes and their possible applications in water and wastewater treatment. Different configurations of photocatalytic membrane reactors (PMRs) are described and characterized. They include PMRs with photocatalyst immobilized on/in the membrane and reactors with catalyst in suspension. Advantages and disadvantages of the hybrid photocatalysis-membrane processes in terms of permeate flux, membrane fouling and permeate quality are discussed. Moreover, a short introduction to the heterogeneous photocatalysis and membrane processes as unit operations is given. [Copyright &y& Elsevier]

Abstract: The paper reports investigations on the application of anatase-phase TiO2 for the removal of azo dyes in a hybrid system coupling photocatalysis with direct contact membrane distillation (DCMD, MD). The process was conducted in a laboratory-scale installation equipped with a PP capillary module. The influence of reaction temperature and initial concentration of azo dyes on the effectiveness of their photodegradation was especially investigated. Two mono-azo dyes: Acid Red 18 (AR18) and Acid Yellow 36 (AY36) and one poly-azo dye, Direct Green 99 (DG99) were applied as model compounds. The increase of the reaction temperature from 313 to 333K resulted in an improvement of the efficiency of photodecomposition of the dyes, as was found on the basis of changes of their masses in the feed solution. The comparison of the results obtained during photocatalysis alone and hybrid photocatalysis–MD process revealed that the reduction of feed volume in MD did not affect the photodegradation rate of the azo dyes. An improvement of the effectiveness of the degradation of dyes was obtained by an application of solutions with lower initial concentration (10 instead of 30mg/dm3). Regardless of the process parameters applied, the product (distillate) was almost pure water with conductivity lower than 0.3mS/m and pH above 5.2. [Copyright &y& Elsevier]

Abstract: The presented studies have focused on application of a new anatase-phase TiO2 for decomposition of azo dye Acid Red 18 in a photocatalytic membrane reactor (PMR) combining photocatalysis and direct contact membrane distillation (DCMD). The catalyst used in this study (A-700-1h) was prepared from TiO2 obtained directly from the production line (sulfate technology) at the Chemical Factory “Police” by calcination for 1 h at 973K in air. It was found that the effectiveness of the model dye degradation increased with increasing the value of all the parameters investigated, that is, feed flow rate, reaction temperature and catalyst loading. The addition of TiO2 to a feed did not affect the permeate flux, regardless of the catalyst loading applied. The effectiveness of azo dye removal in the PMR was compared with the effectiveness obtained during photocatalysis alone conducted in the recirculation and batch modes. Taking into account both, the rate of azo dye degradation and the quality of the product, the most beneficial configuration seems to be the PMR. [Copyright &y& Elsevier]

Abstract: An application of a newly prepared TiO2 having anatase phase (A-700-1h) for decomposition of azo dye Acid Red 18 (AR18) in a photocatalytic membrane reactor (PMR), coupling photocatalysis and membrane distillation (MD) was investigated. The effectiveness of decomposition of the model dye using two commercially available TiO2 photocatalysts – ST-01 and P25 was also determined in order to compare the results. The A-700-1h catalyst was prepared from a crude amorphous TiO2 obtained directly from the production line (sulfate technology) at the Chemical Factory “Police” (Poland) by calcination for 1h at 700°C in air. The hybrid photocatalysis–MD process was conducted in a laboratory-scale installation with a capillary module equipped with polypropylene membranes. It was found that the initial degradation rate r 0 of AR18 using the A-700-1h catalyst was 49–64% higher than in case of anatase ST-01. Moreover, the effectiveness of decolorization of the dye solution at the A-700-1h loading of 0.5g/dm3 determined on the basis of r 0 value was only ca. 8% lower compared to the value determined for the P25 photocatalyst. Taking into account the composition of permeate it was found that only a small amount of by-products of dye photodecomposition was transported through the MD membrane. Moreover, a complete retention of the model dye was observed. [Copyright &y& Elsevier]

Abstract: The photocatalytic degradation of natural organic matter (NOM) would be an attractive option in the treatment of drinking water. The performance of a submerged photocatalytic membrane reactor (PMR) was investigated with regard to the removal of NOM and the control of membrane fouling. In particular, this work focused on the adsorption and desorption of humic acids (HA) and lake water NOM at the surface of TiO2 photocatalyts and ferrihydrite (FH) adsorbents in the PMR for water treatment. The addition of FH particles with a large sorption capacity helped remove the NOM released from TiO2 particles, but FH suspended in water affected the photocatalysis of lake water NOM with a low specific UV absorbance (SUVA) value. To prevent the UV light being scattered by FH without any photocatalytic activity, FH particles were attached to a submerged microfiltration (MF) membrane, which contributed to a greater removal of NOM during long-term PMR operation. The further removal of NOM from aqueous solution was achieved due to the synergistic effect of TiO2 photocatalysis and FH adsorption in PMR while minimizing the influence of photoinduced desorption of NOM. No significant membrane fouling occurred when the submerged PMR was operated even at high flux levels (>25L/m2 h), as long as photocatalytic decomposition took place. [Copyright &y& Elsevier]

Photodegradation tests with continuous mode were carried out in a photocatalytic reactor containing a submerged flat sheet non-woven fabric membrane, which was able to retain the photocatalyst. The non-woven fabric membrane was made of polypropylene with a pore size of 2 µm. In this study, three operational parameters were investigated: light intensity, feed concentration, and feed flow rate. Experimental results showed no significant variation of permeate flux and TMP (transmembrane pressure) during the experimental period. The SS (suspended solid) of the permeate was non-detectable. These behaviors were due to the formation of a dynamic porous cake layer on the non-woven fabric membrane surface in our experimental condition. We also found that it was important to control the operation parameter mentioned above as to exactly when we wanted to maintain the steady pollutant concentration in the permeate at very low value. [ABSTRACT FROM AUTHOR]

Abstract: An investigation of the application of the hybrid processes photocatalysis–ultrafiltration (UF) and photocatalysis–membrane distillation (MD) for degradation of an azo-dye in an aqueous solution is presented. Acid Red 18 was applied as a model dye and titanium dioxide Aeroxide® P25 (Degussa, Germany) was used as a photocatalyst. It was found that the photocatalyst was completely separated in the membrane processes applied. However, during UF a significant flux decline due to membrane fouling caused by TiO2 particles was observed. During 5 h of the process performance, the permeate flux was constant, but lower for ca. 25% in comparison with the maximum permeate flux (i.e., when distilled water was applied as a feed). Moreover, the products and byproducts of photodegradation of model azo-dye passed completely through the UF membrane. The results obtained during the combined processes of photocatalysis–MD were much more promising. After 5 h of the processes performance, the model dye was removed completely, whereas TOC concentration was lowered by ca. 80%. [Copyright &y& Elsevier]

The research on photocatalytic membrane reactors (PMRs) started around the year 2000 with the study of wastewater treatment by degradation reactions of recalcitrant organic pollutants, and since then the evolution of our scientific knowledge has increased significantly, broadening interest in reactions such as the synthesis of organic chemicals. In this paper, we focus on some initial problems and how they have been solved/reduced over time to improve the performance of processes in PMRs. Some know-how gained during these last two decades of research concerns decreasing/avoiding the degradation of the polymeric membranes, improving photocatalyst reuse, decreasing membrane fouling, enhancing visible light photocatalysts, and improving selectivity towards the reaction product(s) in synthesis reactions (partial oxidation and reduction). All these aspects are discussed in detail in this review. This technology seems quite mature in the case of water and wastewater treatment using submerged photocatalytic membrane reactors (SPMRs), while for applications concerning synthesis reactions, additional knowledge is required. [ABSTRACT FROM AUTHOR]

Photocatalytic organic synthesis/conversions and water treatment under visible light are a challenging task to use renewable energy in chemical transformations. In this review a brief overview on the mainly employed visible light photocatalysts and a discussion on the problems and advantages of Vis-light versus UV-light irradiation is reported. Visible light photocatalysts in the photocatalytic conversion of CO2, conversion of acetophenone to phenylethanol, hydrogenation of nitro compounds, oxidation of cyclohexane, synthesis of vanillin and phenol, as well as hydrogen production and water treatment are discussed. Some applications of these photocatalysts in photocatalytic membrane reactors (PMRs) for carrying out organic synthesis, conversion and/or degradation of organic pollutants are reported. The described cases show that PMRs represent a promising green technology that could shift on applications of industrial interest using visible light (from Sun) active photocatalysts. [ABSTRACT FROM AUTHOR]

The objectives of the current study are to assess and compare the performance of a developed photocatalytic membrane reactor (PMR) in treating industrial waste (e.g., organic dye waste) against membrane distillation. The current PMR is composed of a feed tank, which is a continuous stirred photocatalytic reactor containing slurry Titanium dioxide (TiO2) particles that are activated by using ultraviolet lamp irradiation at a wavelength of 365 nm, and a poly-vinylidene flouride (PVDF) membrane cell. The experimental setup was designed in a flexible way to enable both separate and integrated investigations of the photocatalytic reactor and the membrane, separately and simultaneously. The experimental work was divided into two phases. Firstly, the PVDF membrane was fabricated and characterized to examine its morphology, surface charge, and hydrophobicity by using a scanning electron microscope, surface zeta potential, and contact angle tests, respectively. Secondly, the effects of using different concentrations of the TiO2 photocatalyst and feed (e.g., dye concentration) were examined. It is found that the PMR can achieve almost 100% dye removal and pure permeate is obtained at certain conditions. Additionally, a kinetic analysis was performed and revealed that the photocatalytic degradation of dye follows a pseudo-first-order reaction. [ABSTRACT FROM AUTHOR]

This paper presents an overview of recent reports on photocatalytic membrane reactors (PMRs) in organic synthesis as well as water and wastewater treatment. A brief introduction to slurry PMRs and the systems equipped with photocatalytic membranes (PMs) is given. The methods of PM production are also presented. Moreover, the process parameters affecting the performance of PMRs are characterized. The applications of PMRs in organic synthesis are discussed, including photocatalytic conversion of CO2, synthesis of KA oil by photocatalytic oxidation, conversion of acetophenone to phenylethanol, synthesis of vanillin and phenol, as well as hydrogen production. Furthermore, the configurations and applications of PMRs for removal of organic contaminants from model solutions, natural water and municipal or industrial wastewater are described. It was concluded that PMRs represent a promising green technology; however, before the application in industry, additional studies are still required. These should be aimed at improvement of process efficiency, mainly by development and application of visible light active photocatalysts and novel membranes resistant to the harsh conditions prevailing in these systems. [ABSTRACT FROM AUTHOR]