Solar Heterogeneous Photocatalysis Research Articles

Kinetic Study of Sodium Dodecylsulfate Degradation by Solar Heterogeneous Photocatalysis Based on Tungsten Oxide

Sodium Dodecyl Sulfate or SDS is a chemical compound widely used in detergent and cosmetic formulations. This work describes the application of solar heterogeneous photocatalysis based on tungsten oxide (WO3) to the kinetic study of the degradation of sodium dodecylsulfate. The experiments were performed at room temperature to study the effect of the initial catalyst mass. The results showed that a small amount of tungsten oxide is sufficient to degrade sodium dodecyl sulfate. The initial concentrations of SDS varied between 5 and 15 mg.L-1. According to the results, more than 87% reduction is obtained after 120 min of solar irradiation of the SDS solution for a WO3/SDS mass ratio of 1/5. The detailed kinetic analysis of the photodegradation of sodium dodecylsulfate showed that the disappearance of the anionic surfactant follows a pseudo-prime model. According to the Langmuir-Hinshelwood model, the kinetics constant calculated from the linear form of this model are : k = 0.042 mg.L.min-1 and K = 0.060 L.mg-1.

Solar photocatalysis using post-consumer alkaline batteries for degrading contaminants of emerging concern in surface water

The goal of this study was to explore the use of post-consumer alkaline batteries' electrolytic paste as photocatalysts in solar processes for degrading contaminants of emerging concern (CECs) in surface water. Two types of alkaline batteries were used: Super Hyper UM-3SHSL8P6 (SH) and Alkaline LR6XAB/4B192 (AK), which were calcined at 500 °C for 4 h. The materials underwent various characterization tests, including SEM, XRF, BET, DRS, TGA, DRX, and pH at the Isoelectric Point (pI). The initial pH and catalysts dose conditions that result in the highest efficiency of methylene blue degradation were achieved through central composite design (CCD), i.e., 11.2, a dose of 1.5 g L−1 for AK and 1.6 g L−1 for SH. After 2 h of exposure to natural solar radiation, SH and AK achieved 72.6% and 96.6% removal efficiency in degrading the methylene blue model substance, respectively. This optimal condition was validated experimentally and statistically. In recycling tests, the photocatalysts maintained their efficiency until the third cycle with no statistically significant differences. The toxicity test with Lactuca sativa (lettuce) seeds showed that the treated water was not toxic. The AK catalyst was tested in the presence of three pharmaceutical drugs (ciprofloxacin, acetaminophen, and carbamazepine) in surface water at optimal pH 11.2 and natural pH (∼7), resulting in an overall removal of approximately 41.3% and 30.6%, respectively. Overall, our findings demonstrate that post-consumer alkaline batteries' electrolytic paste can be a viable option for solar heterogeneous photocatalysis under well-adjusted conditions.

Open-cell ceramic foams covered with TiO2 for the photocatalytic treatment of agro-industrial wastewaters containing imazalil at semi-pilot scale

BackgroundImazalil is a fungicide widely used in postharvest agroindustry, which causes a negative impact on the environment. To remove it from agro-industrial wastewaters, solar heterogeneous photocatalysis, with the photocatalyst fixed onto support, constitutes a promising technique. In this work, two open-cell ceramic foams (with and without carbon) were evaluated as TiO2 supports. Technical and economic feasibility of photocatalysis with TiO2 supported on ceramic foams were assessed. MethodsFoams were covered with TiO2 by dip-coating and subsequent calcination. The obtained systems were characterized by different techniques. Lab-scale removal of imazalil in pure and real water matrices was studied for both materials. The highest performance system was also evaluated at semi-pilot scale. Significant findingsThe C-free support led to the highest photoactivity in both water matrices at lab-scale. No TiO2C synergistic effect was observed due to photon absorption phenomena detected for the support with graphite. The C-free foams coated with TiO2 can be used in solar reactors to decontaminate wastewater with imazalil, achieving 95% degradation and a nontoxic condition for Allivibrio fischeri bacteria at accumulated energy values less than 10 kJ·L−1. This technique can be adapted to each real situation through the adequate selection of the number of photocatalytic converters exposed to sunlight. After economic evaluation, the experimental technology could be considered cost-effective.

Reclamation of wastewater polluted with antihypertensive drug residues by the biological+solar-photocatalytic sequential treatment plant

The quality of polluted wastewater processed by conventional Wastewater Treatment Plants (WWTPs) is in some cases insufficient to reach the degree of purity required. Pharmaceuticals are frequently identified in the aquatic environment, owing to their constant release from WWTPs. Thus, in recent years, they are cataloged as pseudo-persistent pollutants having been recognized as potentially harmful to public health and environmental concern. This work has focused on the removal of 3 antihypertensive pharmaceuticals (furosemide, irbesartan, and valsartan) from aqueous waste solutions using a sequential biological-photocatalytic (TiO2/Na2S2O8) treatment under natural sunlight. Pharmaceutical residues were isolated from water by solid phase extraction (SPE) and analyzed by HPLC-QqQ-MS2. Biodegradation was greater than 65% and 70% for irbesartan and furosemide, respectively, while valsartan was highly biodegradable (> 96%). Next, photocatalytic treatment was applied and just 200 kJ m-2 was required to remove 90 % of micropollutants residues from the effluent. Therefore, the coupling of biological treatment to solar heterogeneous photocatalysis constitutes a valuable instrument to detoxify polluted wastewater.

Removal of Contaminants of Emerging Concern from a Wastewater Effluent by Solar-Driven Heterogeneous Photocatalysis: A Case Study of Pharmaceuticals

The occurrence of emerging micropollutants (pharmaceuticals, pesticides, personal care products, industrial compounds, etc.) in the environment is considered a major threat to human health and aquatic ecosystems. These micropollutants enter the environment through anthropogenic actions and have been identified in surface, ground, waste, and even in drinking water, in quantities ranging from ng L−1 to µg L−1. Currently, the pollution of the global water cycle with persistent organic pollutants remains one of the major challenges of the twenty-first century. Most of these organic substances are only partially removed by conventional wastewater treatment plants. Particularly, considerable amounts of pharmaceuticals are used in human and veterinary medicine, which are not efficiently removed during conventional wastewater treatments and subsequently continuously enter freshwater systems and even agricultural crops. Accordingly, we have evaluated the effectivity of TiO2 as a photocatalyst in tandem with Na2S2O8 as an oxidant for the treatment of a wastewater effluent polluted with pharmaceutical (atenolol, carbamazepine, clarithromycin, erythromycin, irbesartan, and ketoprofen) residues. Results show that the use of solar heterogeneous photocatalysis by means of band-gap semiconductor materials, especially TiO2 in combination with a strong oxidant such as Na2S2O8, significantly enhances their disappearance from the wastewater effluent. However, the selected pharmaceuticals show a slow degradation in wastewater effluent compared to pure water indicating that the occurrence of dissolved salts and organic carbon in wastewater effluent noticeably slows down the efficiency of the treatment. A single first-order model satisfactorily explains the photocatalytic degradation of the compounds studied for both, pure and wastewater. In the case of wastewater effluent, the highest DT50 values were observed for macrolides (13 and 16 min for erythromycin and clarithromycin, respectively), while the other compounds studied showed DT50 values below 10 min. This methodology has a notorious interest in some areas of the Mediterranean basin with water shortage, such as SE of Spain, where more than 3000 h of sunlight per year are recovered.

Removal assessment of disinfection by-products (DBPs) from drinking water supplies by solar heterogeneous photocatalysis: A case study of trihalomethanes (THMs)

Solar heterogeneous photocatalysis was used to remove trihalomethanes (THMs) from drinking water. THMs, mainly trichloromethane (TCM), tribromomethane (TBM), bromodichloromethane (BDCM) and dibromochloromethane (DBCM) are one of the main class of disinfection by-products (DBPs). THMs were determined by HSGC-MS with detection limits (LODs) ranging from 0.5 μg L−1 to 0.9 μg L−1 for TCM and BDCM, respectively. Results show that a great proportion of THMs present in water are finally transferred to air as a result of their high volatility in the order TCM > BDCM > DBCM > TBM. The use of band-gap semiconductor materials (TiO2 and mainly ZnO) used as photocatalysts in combination with Na2S2O8 as electron acceptor and sulfate radical anion (SO4•-) generator enhanced the photooxidation of all THMs as compared to photolytic test. The time required for 50% of THMs to disappear (DT50) from water calculated for the most effective treatment (ZnO/Na2S2O8) were 12, 42, 57 and 61 min for TCM, TBM, BDCM, and DBCM, respectively. Therefore, solar heterogeneous photocatalysis can be considered as an interesting strategy for THMs removal, especially in sunny areas like Mediterranean basin.

Arsenite to Arsenate Oxidation and Water Disinfection via Solar Heterogeneous Photocatalysis: A Kinetic and Statistical Approach

Arsenic (As) poses a threat to human health. In 2014, more than 200 million people faced arsenic exposure through drinking water, as estimated by the World Health Organization. Additionally, it is estimated that drinking water with proper microbiological quality is unavailable for more than 1 billion people. The present work analyzed a solar heterogeneous photocatalytic (HP) process for arsenite (AsIII) oxidation and coliform disinfection from a real groundwater matrix employing two reactors, a flat plate reactor (FPR) and a compound parabolic collector (CPC), with and without added hydrogen peroxide (H2O2). The pseudo first-order reaction model fitted well to the As oxidation data. The treatments FPR–HP + H2O2 and CPC–HP + H2O2 yielded the best oxidation rates, which were over 90%. These treatments also exhibited the highest reaction rate constants, 6.7 × 10−3 min−1 and 6.8 × 10−3 min−1, respectively. The arsenic removal rates via chemical precipitation reached 98.6% and 98.7% for these treatments. Additionally, no coliforms were detected at the end of the process. The collector area per order (ACO) for HP treatments was on average 75% more efficient than photooxidation (PO) treatments. The effects of the process independent variables, H2O2 addition, and light irradiation were statistically significant for the AsIII oxidation reaction rate (p < 0.05).

Reclamation of aqueous waste solutions polluted with pharmaceutical and pesticide residues by biological-photocatalytic (solar) coupling in situ for agricultural reuse

This work focuses on the detoxification of aqueous waste solutions polluted with 24 emerging pollutants (13 pharmaceuticals and 11 pesticides) using a coupled biological-photocatalytic facility under natural sunlight for use in crop irrigation. The polluted wastewater (urban, agricultural, and industrial) processed by conventional wastewater treatment plants is in some cases insufficient to reach the degree of purity required. This concern is of particular interest, especially in areas where a low rainfall pattern provides insufficient water resources to meet the demands caused by agriculture, which requires increased reuse of wastewater effluents. For this purpose, polluted water was first subjected to biological treatment followed by a photocatalytic process using the tandem TiO2/Na2S2O8. Residues of pharmaceuticals and pesticides were isolated by solid phase extraction (SPE) and analysed by HPLC-QqQ-MS2. A notorious removal of pharmaceuticals was observed after biological treatment (average removal = 78%), except for diclofenac (31%) and carbamazepine (1%). In a contrary way, biodegradation of pesticides was inconspicuous (average removal = 48%) due to their recalcitrant properties. However, all compounds were rapidly degraded during the photocatalytic treatment because the fluence (H) required to obtain 90% degradation (H90) was<470 kJ m−2 for the most persistent pollutant (terbuthylazine). Single first order kinetic model satisfactorily explained the photooxidation of all micropollutants. Therefore, solar heterogeneous photocatalysis is presented as a promising technology to be incorporated as a tertiary process in wastewater treatment plants to remove biorecalcitrant pollutants. This implementation could be interesting especially in arid and semi-arid areas characterised by water scarcity but receiving many hours of sunshine per year, where a high percentage of reclaimed water is used for crop irrigation.

Comparative Efficiencies for Phenol Degradation on Solar Heterogeneous Photocatalytic Reactors: Flat Plate and Compound Parabolic Collector

Phenol is a recalcitrant anthropogenic compound whose presence has been reported in both wastewater and drinking water; human exposure to phenolic substances can lead to health problems. The degradation of phenol (measured as COD decrease) through solar heterogeneous photocatalysis with immobilized TiO2 was performed in two different reactors: a flat-plate reactor (FPR) and a compound parabolic collector (CPC). A 23 full factorial experimental design was followed. The variables were the presence of TiO2, H2O2 addition, and the type of reactor. Data were fitted to the pseudo-first-order reaction-rate-kinetics model. The rate constant for photocatalytic phenol degradation with 1 mM of H2O2 was 6.6 × 10−3 min−1 for the FPR and 5.9 × 10−3 min−1 in the CPC. The calculated figures of merit were analyzed with a MANCOVA, with UV fluence as a covariate. An ANCOVA showed that the type of reactor, H2O2 addition, or fluence had no statistically significant effect on the results, but there was for the presence of TiO2. According to the MANCOVA, fluence and TiO2 presence were significant (p &lt; 0.05). The CPC was on average 17.4% more efficient than the FPR when it came to collector area per order (ACO) by heterogeneous photocatalysis and 1 mM H2O2 addition.

Binary Mixtures of ZnO/TiO2 for Solar Heterogeneous Photocatalysis of Non-Purgeable Organic Carbon in Landfill Leachate

Landfill leachate is a global problem that has attracted considerable attention from researchers in different areas. It is crucial to develop optimized treatment strategies for landfill leachate, given the need to minimize or eliminate negative environmental impacts resulting from the inadequate disposal of solid waste, as determined by legislation. Landfill leachate is primarily composed of humic substances, which may associate with other toxic molecules and are recalcitrant to the conventional treatments used in Brazil. This study assessed the photocatalytic degradation of carbonaceous materials in leachate collected from the Cachoeira Paulista municipal landfill, São Paulo State, Brazil. Sunlight was used as energy source without additional light inputs. Experiments were carried out in a thin-film fixed-bed reactor, using metal plates coated with paints formulated for this purpose. Paints had a low additives loading, including that of photocatalysts. We investigated the photocatalytic behavior of the binary system ZnO/TiO2 incorporated into acrylic varnish in the degradation of non-purgeable organic carbon (NPOC) in samples of humic acids and fulvic acids + humins. Reactions were conducted under acidic, neutral, or alkaline conditions. NPOC degradation was low in fulvic acid + humin samples, regardless of photocatalyst concentration or pH. The proposed process resulted in high degradation of humic acids, especially under conditions of low chemical stability, which facilitated oxidation. A maximum humic acid degradation of 65% was achieved using high concentrations of TiO2 in acidic medium.

Removal Kinetics of Four Leacher Herbicides Through Solar Heterogeneous Photocatalysis as Influenced by Water Matrix Components

This work focuses on the effect of dissolved substances on the photocatalytic degradation of four herbicides, metribuzin and terbuthylazine (triazine) and chlorotoluron and isoproturon (phenylurea) in three different water matrix (deionized, mineral and leaching water). To study the effect of heterogeneous photocatalysis on their degradation, TiO2 and ZnO were used as photocatalysts in tandem with an oxidant (Na2S2O8). Results show that the addition of both semiconductor materials significantly enhances degradation of the herbicides although in different proportions. Similar effectivity of both photocatalyst, assessed as a function of the mean half-lives calculated, was observed (85 and 87min for TiO2 and Zn, respectively), while the mean half-life in the photolytic experiment was markedly higher (265min). The degradation rate was in the order: metribuzin > chlorotoluron ≈ isoproturon > terbuthylazine. A faster degradation was observed in all cases in deionized water as compared to mineral and leaching water indicating that the presence of dissolved salts and organic matter considerably slows down the effectiveness of the treatment. Although after 180min of treatment, total mineralization was not achieved in mineral and leaching water, this technology considerably reduces the pollutant load in complex water matrices. Therefore, solar heterogeneous photocatalytic processes, especially those involving ZnO and TiO2 as photocatalysts, offers a valuable tool for surface and groundwater remediation, especially in those areas receiving a large number of hours of sunshine per year.

Zero-degree photochemical synthesis of highly dispersed Pt/TiO2 for enhanced photocatalytic hydrogen generation

Pt nanoparticles supported on TiO2 is found to be active for solar heterogeneous photocatalysis. However, the tendency of Pt nanoparticles to grow/aggregate into larger secondary particles in the photochemical synthesis is an obstruction for good performance. Temperature can modulate the size and electronic properties of Pt particles from synthesis in solution. Unlike high temperature, photochemical solution-phase reaction at low temperature leads to a sluggish diffusion-controlled nucleation and growth kinetics, which holds great promise to suppress aggregation. Herein, we report a zero-degree photochemical synthesis to obtain a highly dispersed Pt/TiO2 catalyst at an impressive hydrogen generation rate of 643.29 mmol g−1 h−1 and good stability upon solar light illumination, superior to the counterparts at room temperature (25 °C) or even higher solution-phase temperature (60 °C). Comparative characterizations evidence that zero-degree photochemical synthesis prefers small stable Pt nanoparticles to promote photoelectron transfer and collection, which provides an experimental guideline for constructing advanced photocatalysts.

Solar-Induced Removal of Benzophenones Using TiO2 Heterogeneous Photocatalysis at Lab and Pilot Scale

This work presents the main results regarding the use of solar heterogeneous photocatalysis with TiO2 on the removal of Benzophenone-1 and Benzophenone-2 (BP1 and BP2) in aqueous samples at lab and pilot scale. BP1 and BP2 are two UV-filters that have been classified as potential endocrine disruptors, and their presence in water has been reported by different researches. Experiments were conducted at lab scale using simulated sunlight radiation, while at pilot scale a solar compound cylinder-parabolic (CCP) collector and direct sunlight were employed. Effects of catalyst concentration and solution pH on contaminants elimination were assessed. Pollutants were completely removed at lab conditions in just 60 min of reaction, while under pilot scale tests elimination was around 90.0% in 360 min. Mineralization of treated samples was around 60%. In general, it was found that the photo-generation of hydroxyl (HO·) radicals contributes to BP1 and BP2 removal, and that higher doses of TiO2 could have an inhibitory effect. Additionally, presence of some inorganic ions on the aqueous matrix (drinking water) used in the pilot-scale tests would be associated to a reduction on the extent of pollutants degradation, which together with aspects such as the type of reactor and the atmospheric and climate conditions would limit the process efficiency in comparison with results at lab-scale experiments.

Characterization and Comparative Performance of TiO2 Photocatalysts on 6-Mercaptopurine Degradation by Solar Heterogeneous Photocatalysis

The crystallographic properties of two titanium dioxide (TiO2) photocatalysts, P25, and commercial C1-TiO2 reactive grade, were analyzed by X-ray diffraction (XRD) and the band-gap was calculated with UV–Vis spectrometry with integration sphere. Then, their performance was tested in the degradation of 6-mercaptopurine (6-MP) by heterogeneous photocatalysis with solar radiation under different pH conditions and the addition of hydrogen peroxide (H2O2); the degradation efficiency was monitored by UV–Vis spectrophotometry. The XRD analysis showed that both photocatalysts studied have anatase phase, while only P25 contains rutile; the band gap values were lower, in both catalysts, than those reported for catalysts obtained by the sol-gel method. With both photocatalysts, degradation experiments showed efficiency greater than 98% in experiments in the presence of H2O2 regardless of pH. The properties of the photocatalysts, along with the data obtained from the experimentation, helped determine the best semiconductor for the degradation of 6-MP with these operating conditions in this work.

Solar-driven photocatalytic treatment as sustainable strategy to remove pesticide residues from leaching water.

We have demonstrated the potential leaching of eight compounds, one insecticide (flonicamid) and seven fungicides (myclobutanil, penconazole, boscalid, difenoconazole, trifloxystrobin, pyraclostrobin and fenpyroximate) trough a typical Mediterranean soil (Calcaric regosol). The concentrations found in leaching water were in all cases above the limit set by the EU in groundwater (0.1μgL-1). For this, the efficiency of different homogeneous (photo-Fenton and photo-Fenton-like) and heterogeneous (ZnO and TiO2) photocatalytic systems was tested in deionized water to choose the most appropriate treatment to remove pesticide residues from leaching water. The efficiency was in the order: ZnO + S2O82- (pH7) > TiO2+ S2O82- (pH7) > ZnO (pH7) > TiO2 (pH7) > Fe3+ (pH3) > Fe3+ (pH5) > Fe2+ (pH3) > Fe2+ (pH5). Thus, in the subsequent experiment we focus on the efficacy of solar heterogeneous photocatalysis (ZnO/Na2S2O8 and TiO2/ Na2S2O8) on their removal from leaching water. A fast removal was observed for all pesticides at the end of the photoperiod, noticeably higher in the case of ZnO system, with the exception of flonicamid, a recalcitrant pesticide where the degradation rate only reached about 20% after 240min of solar exposure. Although the mineralisation of the initial dissolved organic carbon was not complete due to the presence of interfering substances in the leaching water, the conversion rate under ZnO/Na2S2O8 treatment was about 1.3 times higher than using TiO2/Na2S2O8.

Oxygen vacancies mediated charge separation and collection in Pt/WO3 nanosheets for enhanced photocatalytic performance

Solar heterogeneous photocatalysis is a highly desirable way for the degradation of volatile organic compounds. Controlled creation of intrinsic oxygen vacancies can significantly modulate the optical and electronic properties of metal oxide semiconductors. However, poor charge utilization in defective metal oxides restrains their photocatalysis efficiency by the sluggish interfacial reaction dynamics. Herein, we demonstrate an effective photogenerated carriers collection for VOCs oxidation by mean of broadband light absorption and unidirectional electron flow to surface reactive sites by synergetic contribution of Pt nanoparticles acting as electron trapping and WO3 with abundant oxygen vacancies via facile one-step room-temperature NaBH4 treatment strategy. The optimized Vo-rich (oxygen vacancies-rich) Pt/WO3 nanosheets is able to achieve effective charge carrier utilization in a high toluene conversion of 98% even at a high CO2 yield of 95% with a quantum efficiency of 55.7% and good stability under solar light irradiation. This work highlights using oxygen vacancies-rich semiconductor as a promising support to design efficient and durable photocatalyst with collaborative optimizing charge separation and utilization, which will provide valuable insights on the defect engineering for photoredox catalysis applications toward efficient solar-to-chemical energy conversion.

Removal of Pesticides with Endocrine Disruptor Activity in Wastewater Effluent by Solar Heterogeneous Photocatalysis Using ZnO/Na2S2O8

The solar photocatalysis has received increasing attention in the last years due to its great potential as eco-friendly technology to detoxify wastewater polluted with estrogenic and/or androgenic chemicals. In this context, this study aims to demonstrate the photocatalyzed degradation of two fungicides (vinclozoline and fenarimol) and four insecticides (malathion, fenotrothion, quinalphos, and dimethoate) all of them with endocrine-disrupting activity, in a wastewater effluent under natural sunlight and pilot plant scale. For this, we have combined hydroxyl radical (HO•)- and sulfate radical (SO4●−)-based advanced oxidation processes (AOPs) by using of ZnO as photocatalyst and Na2S2O8 as oxidant, respectively. Previously, catalyst loading, effect of electron acceptor, and pH conditions were optimized using a lab photoreactor under artificial light. As a result, 200 mg L−1 of ZnO and 250 mg L−1 of Na2S2O8 were used in the further experiment at pilot plant scale at pH around 7. The results show that the use of the tandem ZnO/Na2S2O8 strongly enhances the reaction rate of the studied pesticides as compared with the photolytic test. All pesticides followed an apparent first-order degradation curve. The necessary time for 90% degradation (DT90) under sunlight irradiation ranged from 26 to 1000 min (2–75 min as normalized illumination time, t30W) for malathion and fenarimol, respectively. At the end of the lighting, the remaining percentage of dissolved organic carbon (DOC) was up to 92% lower than its initial content and toxicity (Vibrio fischeri) decreased from 65% of inhibition to an acceptable value of 12% at the end of the treatment. A weak increase in the electrical conductivity (EC) was observed due to the mineralization process. The findings confirm the efficacy of the treatment to remove pesticides from wastewater using natural sunlight as renewable energy source, mainly in sunny areas as Mediterranean basin.

Solar heterogeneous photocatalysis (ZnO/UV) for textile dyes removal

AbstractSolar photocatalytic studies were carried out using zinc oxide (ZnO) as a catalyst for the removal of the cationic methylene blue (MB) dye, and the anionic dye reactive red 198 (RR198), from simple and binary mixed solutions. The following parameters were experimentally investigated: catalyst concentrations (50–250 milliliters [ml]), initial pH of the solution (5, 7, and 9), and time of exposure (20–120 minutes [min]). The catalyst concentration has been found to be the variable with the greatest significance of the three, leading to degradation rates of up to 98% and 100%, for MB and RR198 dyes, respectively. When it comes to the RR198 dye, considerable decolorization rates (up to 75%) were achieved even at the shortest time interval (20 min). The results indicated that, especially for the RR198 dye, the majority of the color removal during the photocatalysis process was due to the adsorption of the dye onto the ZnO surface. Batch scale experiments were performed by mixing both MB and RR198 dyes in order to simulate a synthetic effluent. Color removal rates up to 98% were achieved after 90 min of sunlight exposure. Experiments in a pilot‐plant based on compound parabolic collectors were performed under the same conditions, and similar results were obtained. In addition, organic matter removal was investigated and rates up to 70% were achieved. The results showed the feasibility of the solar photocatalysis process with ZnO to achieve considerable rates of color removal from wastewater containing dyes from different classes.

A Novel Prototype Offset Multi Tubular Photoreactor (OMTP) for solar photocatalytic degradation of water contaminants

The design and operation of a new solar photoreactor prototype named Offset Multi Tubular Photoreactor (OMTP) is presented. The OMTP advances over the compound parabolic collector (CPC) photoreactor, which is one of the most efficient design for large-scale solar detoxification of water and wastewater. The OMTP design is based on a simple modification of the common CPC and included a supplementary set of tubes in the space occupied by the axes of intersection of the CPC reflective involutes. This new reactor configuration increased the irradiated reactor volume by 79% and the fluid residence time by up to 1.8-fold in comparison to the CPC, for the same solar irradiated area (footprint). The model parameters used for comparing and scaling the OMPT and CPC were β (reactor volume/total volume), α (area of absorption/total volume), αg (physical area/total volume), degradation efficiency ηα per unit area, and the operating volume. The total solar energy absorbed in the reactors (1.74 m2 footprint) was 15.17 W for the CPC and 21.86 W for the OMTP, which represents an overall gain of 44% for the latter. The performance of the OMTP and CPC were compared at the same value of solar exposure, β of 0.3 with optimal photocatalyst loading of 0.25 g/L titanium dioxide (TiO2 P25). The degradation efficiencies of methylene blue, dichloroacetic acid, 4-chlorophenol (120 ppm initial concentration) in the OMTP were up to 81%, 125%, 118% and 242% higher, respectively, in comparison to the CPC after 8000 J/m2 of accumulated solar energy. The OMTP should outperform the CPC in environmental and renewable energy applications of solar heterogeneous photocatalysis.

Kinetic study of food dyes removal from aqueous solutions by solar heterogeneous photocatalysis with artificial neural networks and phytotoxicity assessment

Kinetic study of food dyes removal from aqueous solutions by solar heterogeneous photocatalysis with artificial neural networks and phytotoxicity assessment