Slurry photocatalytic membrane reactor technology for removal of pharmaceutical compounds from wastewater: Towards cytostatic drug elimination

Heterostructure g-C3N4/Bi2MoO6 PVDF nanofiber composite membrane for the photodegradation of steroid hormone micropollutants

Photocatalytic membrane reactors (PMRs) are a promising technology for micropollutant removal. Sunlight utilization and catalyst surface sites limit photodegradation. A poly(vinylidene fluoride) (PVDF) nanofiber composite membrane (NCM) with immobilized visible-light-responsive g-C3N4/Bi2MoO6 (BMCN) were developed. Photodegradation of steroid hormones with the PVDF-BMCN NCM was investigated with varying catalyst properties, operating conditions, and relevant solution chemistry under solar irradiation. Increasing CN ratio (0-65 %) enhanced estradiol (E2) degradation from 20 ± 10 to 75 ± 7 % due to improved sunlight utilization and photon lifetime. PVDF nanofibers reduced self-aggregation of catalysts. Hydraulic residence time and light intensity enhanced the photodegradation. With the increasing pH value, the E2 removal decreased from 84 ± 4 to 67 ± 7 % owing to electrical repulsion and thus reduced adsorption between catalysts and E2. A removal of 96 % can be attained at environmentally relevant feed concentration (100 ng.L-1) with a flux of 60 L.m-2.h-1, irradiance of 100 mW.cm-2, and 1 mg.cm-2 BMCN65 loading. This confirmed that heterojunction photocatalysts can enhance micropollutants degradation in PMRs.

Anticancer drugs in wastewater and natural environments: A review on their occurrence, environmental persistence, treatment, and ecological risks

The consumption of anticancer drugs (also known as chemotherapy drugs or antineoplastic drugs) has augmented over the last decades due to increased cancer incidence. Although there is an increasing concern about the presence of pharmaceutical compounds in natural environments and urban/domestic wastewater, anticancer drugs used in chemotherapy and anticancer medication have received less attention. In this review, the occurrence, environmental persistence, and known and potential ecological impacts of anticancer drugs is discussed. This review shows that these compounds are being increasingly detected in effluents of hospitals, influents and effluents of wastewater treatment plants, river surface water and sediments, groundwater, and even drinking water. Anticancer drugs can impact aquatic organisms such as algae, crustaceans, rotifers, and fish and may promote changes in soil and water microbial communities that may alter ecosystem functioning. Our knowledge of technologies for the removal of anticancer drugs is still limited, and these drugs can be dispersed in nature in a diffuse way in an uncontrolled manner. For this reason, an improved understanding of the presence, persistence, and ecological impacts of anticancer drugs in wastewater and natural environments is needed to help design management strategies, protect aquatic microorganisms, and mitigate potential ecological impacts.

Decentralized systems for the treatment of antimicrobial compounds released from hospital aquatic wastes

In many developing countries, untreated hospital effluents are discharged and treated simultaneously with municipal wastewater. However, if the hospital effluents are not treated separately, they pose concerning health risks due to the possible transport of the antimicrobial genes and microbes in the environment. Such effluent is considered as a point source for a number of potentially infectious microorganisms, waste antimicrobial compounds and other contaminants that could promote antimicrobial resistance development. The removal of these contaminants prior to discharge reduces the exposure of antimicrobials to the environment and this should lower the risk of superbug development. At an effluent discharge site, suitable pre-treatment of wastewater containing antimicrobials could maximise the ecological impact with potentially reduced risk to human health. In addressing these points, this paper reviews the applications of decentralized treatment systems toward reducing the concentration of antimicrobials in wastewater. The most commonly used techniques in decentralized wastewater treatment systems for onsite removal of antimicrobials were discussed and evidence suggests that hybrid techniques should be more useful for the efficient removal of antimicrobials. It is concluded that alongside the cooperation of administration departments, health industries, water treatment authorities and general public, decentralized treatment technology can efficiently enhance the removal of antimicrobial compounds, thereby decreasing the concentration of contaminants released to the environment that could pose risks to human and ecological health due to development of antimicrobial resistance in microbes.

The potential application of bio-based ceramic/organic xerogel derived from the plant sources: A new green adsorbent for removal of antibiotics from pharmaceutical wastewater

A bio-based ceramic/organic xerogel (BCO-xerogel) was obtained from the combination of sugarcane bagasse ash, polyvinyl alcohol, and pine cone-derived tannin extract, which are abundant, non-toxic, and renewable sources. The as-prepared BCO-xerogel was used as a low-cost green adsorbent for the eliminate of four types of the most widely used antibiotics, including amoxicillin (AMX), tetracycline (TC), cefalexin (CLX), and penicillin G (PEN G) residuals from contaminated water. The simultaneous effects conventional variables including adsorbent dosage, antibiotic concentrations, solution pH, and contact time were studied and optimized by central composite design (CCD) under response surface methodology (RSM). Analysis of variance (ANOVA) was employed as a statistical formula to determine the significance of operating environmental conditions and their interactions with 95% confidence limits. Under optimized conditions, the experimental removal efficiencies for AMX, TC, CLX, and PEN G were 98.78 ± 3.25, 99.12 ± 2.52, 98.02 ± 1.98, and 98.42 ± 2.19, respectively. The adsorption isotherms and kinetics were better fitted with Langmuir and pseudo-second-order models, respectively. Thermodynamic studies showed that the adsorption process was endothermic, spontaneous, and occurred by combination of physical and chemical mechanisms. Also, evaluating the ability of BCO-xerogel to adsorptive removal of AMX, TC, CLX, and PEN G antibiotics in real wastewaters showed about 97.4-98.6% adsorption efficiency in river water and about 67.1-71.3% in three hospital effluents. After the adsorption process, the antibiotic-loaded adsorbent was regenerated by NaOH (0.01 mol L^-1), and the reusability tests showed that the removal efficiencies of the antibiotics in the four recovery steps were still above 90%. This work explored the development of green, efficient, and economical bio-adsorbent that can be utilized for the removal of antibiotics from contaminated wastewaters.

Solar-driven photoelectrocatalytic degradation of anticancer drugs using TiO2 nanotubes decorated with SnS quantum dots

In recent years, the growing interest in applying photoelectrocatalysis (PEC) to decompose organic pollutants has resulted in the need to search for new photoelectrode materials with high activity under visible light radiation. The presented research showed an increased photoelectrocatalytic activity under sunlight of Ti/TiO₂ sensitized with SnS quantum dots, obtained by the successive ionic layer adsorption and reaction (SILAR) method. The presence of SnS caused the enhanced absorption of visible irradiation and the reduction of recombination of generated charges by a p-n heterojunction created with the TiO₂. The highest efficiency of photoelectrocatalytic degradation of anticancer drugs (ifosfamide, 5-fluorouracil, imatinib) was achieved for the SnS-Ti/TiO₂ photoelectrode with a SnS quantum dot size from 4 to 10 nm. In addition, a decrease of IF PEC degradation efficiency was observed with increasing pH and with the presence of Cl^-, NO₃^-, HCO₃^- and organic matter in the treated solution. Studies of the PEC mechanism have shown that drug degradation occurs mainly as a result of the direct and indirect action of photogenerated holes on the SnS-Ti/TiO₂ photoelectrode, and the identified degradation products allowed for the presentation of the degradation pathway of IF, 5-FU and IMB. Duckweed (Lemna minor) growth inhibition tests showed no toxicity of the drug solutions after treatment.

TiO2–Zeolite Metal Composites for Photocatalytic Degradation of Organic Pollutants in Water

Immobilization of photocatalysts in porous materials is an approach to significantly minimize the hazards of manipulation and recovery of nanoparticles. Inorganic materials, such as zeolites, are proposed as promising materials for photocatalyst immobilization mainly due to their photochemical stability. In this work, a green synthesis method is proposed to combine TiO2-based photocatalysts with commercial ZY zeolite. Moreover, a preliminary analysis of their performance as photocatalysts for the abatement of organic pollutants in waters was performed. Our results show that the physical mixture of TiO2 and zeolite maintains photocatalytic activity. Meanwhile, composites fabricated by doping TiO2–zeolite Y materials with silver and palladium nanoparticles do not contribute to improving the photocatalytic activity beyond that of TiO2.

Treatment-driven removal efficiency, product formation, and toxicity evolution of antineoplastic agents: Current status and implications for water safety assessment

Antineoplastic compounds, designed for chemotherapeutic anticancer therapy, have become emerging contaminants of global concern over the past decade due to their ubiquitous occurrence, environmental persistence, and multiple adverse effects on aquatic ecosystems. Increasing efforts have been devoted to developing efficient strategies for remediating water containing these micropollutants. In this study, the physicochemical properties, natural attenuation, and chemical reactivity with aqueous oxidizing species of five antineoplastic drugs with the highest environmental prevalence (i.e., tamoxifen, cyclophosphamide, ifosfamide, 5-fluorouracil, and methotrexate) were summarized. The removal performance, transformation products (TPs) of varying structures, overall reaction pathways, and toxicity evolution during different treatments were evaluated and discussed. Additionally, the biodegradability and multi-endpoint toxicity of each TP were predicted using in silico QSAR software. Depending on their distinct inherent structures, the reactivity of the antineoplastics with oxidizing species varied, with hydroxyl radicals exhibiting unparalleled merits in rapid oxidation. Complete elimination of these contaminants was observed during oxidative treatments, but with inadequate mineralization. Notably, the increase in toxicity within multiple processes was determined based on both experimental bioassays and theoretical predictions. This may be attributed to the adverse effects induced by the large number of identified and unknown TPs individually and in combination. Together with the environmental persistence and low biodegradability of most TPs, these results necessitate the application of efficient post-treatments in conjunction with a more thorough water safety evaluation (e.g., using high-throughput screening) of the mixtures of treated water and wastewater.

The Dark Side of Platinum Based Cytostatic Drugs: From Detection to Removal

The uncontrolled release of pharmaceutical drugs into the environment raised serious concerns in the last decades as they can potentially exert adverse effects on living organisms even at the low concentrations at which they are typically found. Among them, platinum based cytostatic drugs (Pt CDs) are among the most used drugs in cancer treatments which are administered via intravenous infusion and released partially intact or as transformation products. In this review, the studies on environmental occurrence, transformation, potential ecotoxicity, and possible treatment for the removal of platinum cytostatic compounds are revised. The analysis of the literature highlighted the generally low total platinum concentration values (from a few tens of ng L−1 to a few hundred μg L−1) found in hospital effluents. Additionally, several studies highlighted how hospitals are sources of a minor fraction of the total Pt CDs found in the environment due to the slow excretion rate which is longer than the usual treatment durations. Only some data about the impact of the exposure to low levels of Pt CDs on the health of flora and fauna are present in literature. In some cases, adverse effects have been shown to occur in living organisms, even at low concentrations. Further ecotoxicity data are needed to support or exclude their chronic effects on the ecosystem. Finally, fundamental understanding is required on the platinum drugs removal by MBR, AOPs, technologies, and adsorption.

A modified membrane filtration-ultraviolet photocatalytic system for the removal of trace sulfadiazine in drinking water (No. CHEM77354R1)

In this paper, the membrane filtration-photocatalytic coupling process was used to explore the mechanism and removal effect of trace concentrations of sulfadiazine (SD) in drinking water. First, 8 kinds of ultrafiltration membranes were successfully prepared, and their performance was verified by scanning electron microscopy and measurement of the contact angle, membrane pure water flux, porosity and average pore size. The results showed that the best-performing membranes were the PVDF-PP-TiO₂-DA (dopamine) (PPT₁D)- and PVDF-PP-TiO₂-FeCl₃ (PPT₂Fe)-modified ultrafiltration membranes, in which TiO₂ was modified with DA and FeCl₃, forming the cooperation of TiO₂/DA and TiO₂/Fe³⁺, with removal rates of 91.4% and 92.6% and quasi-first-order rates of 0.0216 min-1 and 0.0214 min-1. At the same time, the effects of the two types of membrane, UV light and water quality characteristics on the removal performance of the membrane filtration-photocatalytic system were discussed. Among them, the PPT₁D membrane was more suitable than the other membranes for the degradation of weakly alkaline water containing SD (pH = 7.5), except when NO₃^- was present, and the water quality characteristics had a significant inhibitory effect on the removal effect. The PPT₂Fe membrane was more suitable for the degradation of acidic water containing SD (pH = 3). Additionally, the water quality characteristics had an obvious inhibitory effect on the removal effect, and the accuracy of the water distribution experimental results was verified by using an actual body of water. In the end, the reaction mechanism of the filtration-photocatalytic system was proposed, and it was found that OH played an indispensable role in the removal of SD.

Studies of the potential of a native natural biosorbent for the elimination of an anionic textile dye Cibacron Blue in aqueous solution

This work is devoted to the adsorption of Cibacron Blue (CB) an anionic textile dye, on bean peel (BP) an agricultural waste with neither activation nor carbonization. The adsorption was realized in batch configuration at ambient temperature in acidic medium. The adsorbent was characterized by FTIR, SEM and BET analyses; the equilibrium isotherms and kinetics were also studied. It has been found that this waste could be used as a low-cost biosorbent for CB elimination under optimal working conditions. The rate of CB elimination reaches 95% on bean bark (3.6 g/L) at pH 2.2 and a reject concentration of 25 mg/L. The pseudo-second-order describes suitably the experimental data and the external diffusion is the rate-determining step. The Freundlich isotherm fits better the CB adsorption with a correlation coefficient (R²) of 0.94 and an RMSE = 1.5115. The negative enthalpy (ΔH) and free enthalpy (ΔG°) indicate a physical and spontaneous nature of the CB biosorption onto the biomaterial.

Toward Scaling-Up Photocatalytic Process for Multiphase Environmental Applications

Recently, we have witnessed a booming development of composites and multi-dopant metal oxides to be employed as novel photocatalysts. Yet the practical application of photocatalysis for environmental purposes is still elusive. Concerns about the unknown fate and toxicity of nanoparticles, unsatisfactory performance in real conditions, mass transfer limitations and durability issues have so far discouraged investments in full-scale applications of photocatalysis. Herein, we provide a critical overview of the main challenges that are limiting large-scale application of photocatalysis in air and water/wastewater purification. We then discuss the main approaches reported in the literature to tackle these shortcomings, such as the design of photocatalytic reactors that retain the photocatalyst, the study of degradation of micropollutants in different water matrices, and the development of gas-phase reactors with optimized contact time and irradiation. Furthermore, we provide a critical analysis of research–practice gaps such as treatment of real water and air samples, degradation of pollutants with actual environmental concentrations, photocatalyst deactivation, and cost and environmental life-cycle assessment.

Threat and sustainable technological solution for antineoplastic drugs pollution: Review on a persisting global issue

In the past 20 years, the discharge of pharmaceuticals and their presence in the aquatic environment have been continuously increasing and this has caused serious public health and environmental concerns. Antineoplastic drugs are used in chemotherapy, in large quantities worldwide, for the treatment of continuously increasing cancer cases. Antineoplastic drugs also contaminate water sources and possess mutagenic, cytostatic and eco-toxicological effects on microorganisms present in the aquatic environment as well as on human health. Due to the recalcitrant nature of antineoplastic drugs, the commonly used wastewater treatment processes are not able to eliminate these drugs. Globally, various anticancer drugs are being consumed during chemotherapy in hospitals and households by out-patients. These anti-cancer agents enter the water bodies in their original form or as metabolites via urine and faeces of the out-patients or the patients admitted in hospitals. Due to its high lipid solubility, the antineoplastic drugs accumulate in the fatty tissues of the organisms. These drugs enter through the food chain and cause adverse health effects on humans due to their cytotoxic and genotoxic properties. The United States Environmental Protection Agency (US-EPA) and the Organization for Economic Cooperation and Development (OECD) elucidated new regulations for the management of hazardous pharmaceuticals in the water environment. In this paper, the role of antineoplastic agents as emerging water contaminants, its transfer through the food chain, its eco-toxicological properties and effects, technological solutions and management aspects were reviewed.

Removal of sulfadiazine in a modified ultrafiltration membrane (PVDF-PVP-TiO2-FeCl3) filtration-photocatalysis system: parameters optimizing and interferences of drinking water

The addition of Fe³⁺ to TiO₂ is one of the effective methods to inhibit the recombination of photogenerated electrons and holes and thus improve the photocatalytic activity of TiO₂. The effect of PVDF-PVP-TiO₂-FeCl₃ (PPTFe) membrane filtration-photocatalytic system on the removal of trace concentration of sulfadiazine (SD) in water was evaluated. A two-factor four-level experiment was established to optimize 16 self-made modified membranes. The optimal membrane was then characterized in seven tests (SEM, EDS, membrane pure water flux, contact angle, porosity, mean pore size, ATR-FTIR), resulting in the optimal ratio (PPTFe membrane with 1.2 wt%TiO₂ and 0.8 wt%FeCl₃). Compared with the original membrane, the pore number, pore size, permeability, and hydrophilicity of the PPTFe membrane were all enhanced. The removal efficiency (92.63%) of SD by PPTFe membrane filtration-photocatalysis system was investigated. The reaction rate (0.0214 min^-1) of the removal SD of the system was determined according to the pseudo-first-order kinetic model. The removal performance of membrane type, pH, and water quality parameters (Cl^-, SO₄^2-, NO₃^-, HA) on PPTFe membrane filtration-photocatalytic system were also made a deep inquiry. The results reflected that acidic conditions (pH = 3) were beneficial to SD removal, the presence of Cl^-, SO₄^2-, and HA could inhibit SD removal, while the existence of NO₃^- was unaffected. Furthermore, the removal rate of SD in the actual water body was displayed well in this system. Finally, the possible photocatalytic degradation mechanism was proposed.Graphical abstract.

Effective Decolorization of Rhodamine B by a Ti Foam-Based Photocatalytic Membrane Reactor

In this study, a Ti foam-based photocatalytic membrane reactor (PMR) was constructed for rhodamine B (RhB) wastewater decolorization. Ti foam was chosen as a membrane and visible-light-driven C₃N₄ was chosen as a photocatalyst. The results showed that the decolorization efficiency could be up to 100% with a flow rate of 6.93 mL/min when the PMR was applied in the treatment of a 30 mg/L RhB solution and the concentration of C₃N₄ was 1 g/L. pH played an important role in the decolorization performance of the PMR. Alkalinity was not conducive to the decolorization of RhB in the PMR, which was mainly due to the property that RhB was difficult to dissolve in an alkaline solution. Membrane fouling was mainly caused by a C₃N₄ photocatalyst, while the effect of RhB on membrane fouling was negligible. Membrane fouling could be retarded when the PMR was applied for RhB treatment under visible-light irradiation, which was because of photoinduced hydrophilicity of C₃N₄. The membrane flux could be restored to its initial values after simple ultrasonic cleaning and backwashing. This was due to the large difference between the pore size of Ti foam and the particle size of C₃N₄ and the super hydrophilicity of Ti foam and C₃N₄.

Visible-Light Photocatalysts and Their Perspectives for Building Photocatalytic Membrane Reactors for Various Liquid Phase Chemical Conversions

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.

A comprehensive review on contaminants removal from pharmaceutical wastewater by electrocoagulation process

The pharmaceuticals are emergent contaminants, which can create potential threats for human health and the environment. All the pharmaceutical contaminants are becoming enormous in the environment as conventional wastewater treatment cannot be effectively implemented due to toxic and intractable action of pharmaceuticals. For this reason, the existence of pharmaceutical contaminants has brought great awareness, causing significant concern on their transformation, occurrence, risk, and fate in the environments. Electrocoagulation (EC) treatment process is effectively applied for the removal of contaminants, radionuclides, pesticides, and also harmful microorganisms. During the EC process, an electric current is employed directly, and both electrodes are dissoluted partially in the reactor under the special conditions. This electrode dissolution produces the increased concentration of cation, which is finally precipitated as hydroxides and oxides. Different anode materials usage like aluminum, stainless steel, iron, etc. are found more effective in EC operation for efficient removal of pharmaceutical contaminants. Due to the simple procedure and less costly material, EC method is extensively recognized for pharmaceutical wastewater treatment over further conventional treatment methods. The EC process has more usefulness to destabilize the pharmaceutical contaminants with the neutralization of charge and after that coagulating those contaminants to produce flocs. Thus, the review places particular emphasis on the application of EC process to remove pharmaceutical contaminants. First, the operational parameters influencing EC efficiency with the electroanalysis techniques are described. Second, in this review emerging challenges, current developments and techno-economic concerns of EC are highlighted. Finally, future recommendations and prospective on EC are envisioned.

Encapsulation of starch hydrogel and doping nanomagnetite onto metal-organic frameworks for efficient removal of fluvastatin antibiotic from water

Growing interests and efforts have been recently focused on design and assembly of novel hydrogel nanosorbents for removal of drugs from wastewater. Therefore, this work is aimed to immobilize and encapsulate starch hydrogel matrix onto metal organic frameworks (MOFs) and dope with nanomagnetite. The magnetic MOFs-Starch hydrogel (NFe₃O₄@Zn(GA)/Starch-Hydrogel) was synthesized via microwave irradiation process and characterized with high surface area (528.39 m²/g), mesoporous with pore size 2.90 nm and highly crystalline structure. The maximum swelling ratio (1000.0 %) was optimized at pH 10, 180 min and 25 °C. The validity of NFe₃O₄@Zn(GA)/Starch-Hydrogel for adsorptive removal of Fluvastatin statin drug provided maximum equilibrium adsorption capacity 782.05 mg g^-1. The Langmuir isotherm and pseudo-second kinetics models were correlated well with the computed correlation coefficient values 0.9991 and 0.9997, respectively. The validity of NFe₃O₄@Zn(GA)/Starch-Hydrogel for removal of FLV statin drug from real water matrices was confirmed in the range 96.15-99.99 %.

Critical Issues and Guidelines to Improve the Performance of Photocatalytic Polymeric Membranes

Photocatalytic membrane reactors (PMR), with immobilized photocatalysts, play an important role in process intensification strategies; this approach offers a simple solution to the typical catalyst recovery problem of photocatalytic processes and, by simultaneous filtration and photocatalysis of the aqueous streams, facilitates clean water production in a single unit. The synthesis of polymer photocatalytic membranes has been widely explored, while studies focused on ceramic photocatalytic membranes represent a minority. However, previous reports have identified that the successful synthesis of polymeric photocatalytic membranes still faces certain challenges that demand further research, e.g., (i) reduced photocatalytic activity, (ii) photocatalyst stability, and (iii) membrane aging, to achieve technological competitiveness with respect to suspended photocatalytic systems. The novelty of this review is to go a step further to preceding literature by first, critically analyzing the factors behind these major limitations and second, establishing useful guidelines. This information will help researchers in the field in the selection of the membrane materials and synthesis methodology for a better performance of polymeric photocatalytic membranes with targeted functionality; special attention is focused on factors affecting membrane aging and photocatalyst stability.

An overview of photocatalytic degradation: photocatalysts, mechanisms, and development of photocatalytic membrane

Photocatalysis is an ecofriendly technique that emerged as a promising alternative for the degradation of many organic pollutants. The weaknesses of the present photocatalytic system which limit their industrial applications include low-usage of visible light, fast charge recombination, and low migration ability of the photo-generated electrons and holes. Therefore, various elements such as noble metals and transition metals as well as non-metals and metalloids (i.e., graphene, carbon nanotube, and carbon quantum dots) are doped into the photocatalyst as co-catalysts to enhance the photodegradation performance. The incorporation of the co-catalyst which alters the photocatalytic mechanism was discussed in detail. The application of photocatalysts in treating persistent organic pollutants such as pesticide, pharmaceutical compounds, oil and grease and textile in real wastewater was also discussed. Besides, a few photocatalytic reactors in pilot scale had been designed for the effort of commercializing the system. In addition, hybrid photocatalytic system integrating with membrane filtration together with their membrane fabrication methods had also been reviewed. This review outlined various types of heterogeneous photocatalysts, mechanism, synthesis methods of biomass supported photocatalyst, photocatalytic degradation of organic substances in real wastewater, and photocatalytic reactor designs and their operating parameters as well as the latest development of photocatalyst incorporated membrane.

Overview of Photocatalytic Membrane Reactors in Organic Synthesis, Energy Storage and Environmental Applications

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.

A Review on the Synthesis and Characterization of Metal Organic Frameworks for Photocatalytic Water Purification

This review analyzes the preparation and characterization of metal organic frameworks (MOFs) and their application as photocatalysts for water purification. The study begins by highlighting the problem of water scarcity and the different solutions for purification, including photocatalysis with semiconductors, such as MOFs. It also describes the different methodologies that can be used for the synthesis of MOFs, paying attention to the purification and activation steps. The characterization of MOFs and the different approaches that can be followed to learn the photocatalytic processes are also detailed. Finally, the work reviews literature focused on the degradation of contaminants from water using MOF-based photocatalysts under light irradiation.

Utilizations of agricultural waste as adsorbent for the removal of contaminants: A review

In recent years, various industrial activities have caused serious pollution to the environment. Due to the low operating costs and high flexibility, adsorption is considered as one of the most effective technologies for pollutant management. Agricultural waste has loose and porous structures, and contains functional groups such as the carboxyl group and hydroxyl group, so it can be invoked as biological adsorption material. Agricultural waste gets the advantages of a wide range of sources, low cost, and renewable. It has a good prospect for the comprehensive utilization of resources when used for environmental pollution control. This article summarized the current research status of agricultural waste in adsorbing pollutants, which pointed out the influencing factors of adsorption, expounded the adsorption mechanism of biological adsorption and introduced the related parameters of adsorption, proposed the application of adsorbents in engineering including adsorption in liquid and gas phases, at the same time it gave the future development prospect of agricultural waste as adsorbent.

Photoelectrocatalytic vs. Photocatalytic Degradation of Organic Water Born Pollutants

The azo dye Basic Blue 41 was subjected to photocatalytic and photoelectrocatalytic degradation using nanopararticulate titania films deposited on either glass slides or Fluorine doped Tin Oxide (FTO) transparent electrodes. The degradation was carried out by irradiating titania films with weak ultraviolet (UVA) radiation. The degradation was faster when using FTO as a titania support even without bias and was further accelerated under forward electric bias. This result was explained by enhanced electron-hole separation even in the case of the unbiased titania/FTO combination. This system for organic material photocatalytic degradation was also successfully applied to the degradation of the anti-inflammatory drug piroxicam, which demonstrated a well distinguished degradation behavior in going from a plain glass support to unbiased and biased FTO. The degradation pathway of piroxicam has been additionally studied using liquid chromatography-accurate mass spectrometry analysis.

Graphitic carbon nitride based nanocomposites for the photocatalysis of organic contaminants under visible irradiation: Progress, limitations and future directions

Graphitic carbon nitride (g-C₃N₄) has drawn great attention recently because of its visible light response, suitable energy band gap, good redox ability, and metal-free nature. g-C₃N₄ can absorb visible light directly, therefore has better photocatalytic ability under solar irradiation and is more energy-efficient than TiO₂. However, pure g-C₃N₄ still has the drawbacks of insufficient light absorption, small surface area and fast recombination of photogenerated electron and hole pairs. This review summarizes the recent progress in the development of g-C₃N₄ nanocomposites to photodegrade organic contaminants in water. Element doping especially by potassium has been reported to be an efficient method to promote the degradation efficacy. In addition, compound doping improves photodegradation performance of g-C₃N₄, especially Ag₃PO₄-g-C₃N₄ which can completely degrade 10mgL^-1 of methyl orange under visible light irradiation in 5min, with the rate constant (k) as high as 0.236min^-1. Moreover, co-doping enhances the photodegradation rate of multiple contaminants while immobilization significantly improves catalyst stability. Most of g-C₃N₄ composites possess high reusability enabling their practical applications in wastewater treatment. Furthermore, environmental conditions such as solution pH, reaction temperature, dissolved oxygen, and dissolved organic matter all have important effects on the photocatalytic ability of g-C₃N₄ photocatalyst. Future work should focus on the synthesis of innovative g-C₃N₄ nanocomposites for the efficient removal of organic contaminants in water and wastewater.