Heterogeneous Photocatalytic Treatment Research Articles

A Comparison of RML Prion Inactivation Efficiency by Heterogeneous and Homogeneous Photocatalysis.

Prions are proteinaceous pathogens responsible for a variety of devastating diseases in mammals, including scrapie in sheep and goats, chronic wasting disease in cervids, and Creutzfeldt-Jakob disease (CJD) in humans. They are characterized by their exceptional persistence to common inactivation procedures. This applies to all possible sources of prion contamination as prions may be present in the tissues and biological fluids of infected individuals. Hence, efficient prion inactivation procedures are still being sought to minimize the risk of intra- or inter-species transmission. In the past, photocatalytic treatment has been proven to be capable of efficiently oxidizing and inactivating prions. In the present study, the efficacy of homogeneous photo-Fenton-based photocatalysis as well as heterogeneous photocatalysis with TiO2 in reducing RML mouse scrapie infectivity was evaluated. Prion inactivation was assessed by means of a bioassay, and the results were confirmed by in vitro experiments. While the prion infectivity of the RML mouse scrapie was reduced after treatment with the photo-Fenton reagent, the heterogeneous photocatalytic treatment of the same prion strain completely eliminated prion infectivity.

Toxicological assessment of ZnO-Vernonia amygdalina nanoparticle-treated Asa River water in albino rats

Traditional water purification methods are increasingly inadequate, leading to the exploration of novel approaches. This study investigated the application of plant-derived nanomaterials for heterogeneous photocatalytic water treatment using ZnO-Vernonia amygdalina nanoparticles (ZVAN). The study evaluated the efficacy of ZVAN in purifying Asa River water (ARW) and assessed its toxicological profile in rats. Synthesized ZVAN was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). ARW samples were collected according to standard guidelines and their physicochemical and bacteriological properties were analyzed. ARW was treated with ZVAN and alum separately. The effects of both treatments on various hematological, liver, and kidney parameters in albino rats were compared after 30 days of daily administration. The total suspended matter (TSM) levels in untreated and treated ARW exceeded approved standards. ZVAN treatment effectively eliminated cadmium (Cd) from the water (from 0.1 ppm to 0). Thermotolerant coliforms and enteric bacteria were also undetectable in ZVAN-treated samples. Compared to the control group, untreated ARW significantly decreased red blood cell (RBC) count (6.86±0.56 vs 2.75±0.11, p<0.05), hemoglobin (10.68±0.81 vs 3.80±0.22, p<0.05), hematocrit (40.78±2.49 vs 15.15±0.95, p<0.05), white blood cell (WBC) count (9.85±0.73 vs 1.60±0.08, p<0.05) and platelet count (377.75±26.96 vs 55.25±15.78, p<0.05). Additionally, statistically significant differences were observed in enzyme activities between experimental and control groups. This study demonstrates the high level of pollution in ARW. ZVAN treatment significantly reduced pollution and mitigated its associated detrimental effects, with minimal to no observed toxicity compared to alum treatment. These findings suggest the potential of ZVAN as a promising alternative for water purification.

Appraisal of water matrix on the removal of fungicide residues by heterogeneous photocatalytic treatment using UV-LED lamp as light source.

In this study, the photocatalytic degradation of four fungicides, myclobutanil, penconazole and difenoconazole (triazole compounds) and boscalid (carboxamide), has been examined in different aqueous matrices (tap water, irrigation water and two WWPT effluents). Experiments were conducted at laboratory scale with different reagents-zinc oxide (ZnO), titanium dioxide (TiO2), sodium persulphate (Na2S2O8) and the combined systems ZnO/Na2S2O8 and TiO2/Na2S2O8-in water exposed to UV-LED irradiation. Previously, the effect of catalyst and oxidant loading on the disappearance kinetics of the different fungicides was assessed to know maximum degradation efficiency. The influence of water matrices and pesticide loading in removal effectiveness has been evaluated. It was observed a greater efficiency in processes conducted using the tandems ZnO/Na2S2O8 and TiO2/Na2S2O8 in irrigation and tap waters. Results showed that UV-LED are a suitable alternative for tackling the removal of organic pollutants in water.

Synthesis of Petal-Like MnO2 Nanosheets on Hollow Fe3O4 Nanospheres for Heterogeneous Photocatalysis of Biotreated Papermaking Effluent.

Owing to the implementation of increasingly stringent water conservation policies and regulations, the pulp and paper mill industry must make increased efforts to meet the limits for pollutant emissions. The primary pretreatment and secondary biochemical treatment methods used currently generally fail to meet the country-specific environmental regulations, and the wastewater must be processed further even after being subjected to secondary biochemical treatments. In this work, we synthesized Fe3O4/MnO2 nanocomposites (FMNs) with a flower-like structure for use in the heterogeneous photocatalytic treatment of biotreated papermaking wastewater. FMNs1.25, which were formed using a KMnO4/Fe3O4 molar ratio of 1.25, could be separated readily using an external magnetic field and exhibited higher photocatalytic activity than those of the other samples as well as MnO2 and Fe3O4. The effects of various experimental parameters on the photocatalytic activity of FMNs1.25, including the initial pH of the wastewater and the catalyst dosage, were determined. The common chemical oxygen demand (CODCr) reduction rate in the case of this sample reached 56.58% within 120 min at a pH of 3, the CODCr of effluent after treatment was 52.10 mg/L. Further, even under neutral conditions, the CODCr of the treated effluent was below the current limit for discharge in China. Moreover, the nanocomposites exhibited good recyclability, and their catalytic activity did not decrease significantly even after five usage cycles. This study should serve as a platform for the fabrication of effective photocatalysts for the advanced treatment of biotreated papermaking effluent and refractory organic wastewater.

Mesostructured ZnO/Au nanoparticle composites with enhanced photocatalytic activity

Ease of catalyst separation from reaction mixtures represents a significant advantage in heterogeneous photocatalytic wastewater treatment. However, the activity of the catalyst strongly depends on its surface-to-volume ratio. Here, we present an approach based on cylindrical polybutadiene-block-poly(2-vinylpyridine) polymer brushes as template, which can be simultaneously loaded with zinc oxide (ZnO) and gold (Au) nanoparticles. Pyrolytic template removal of the polymer yields in mesostructured ZnO/Au composites, showing higher efficiencies in the photocatalytic degradation of ciprofloxacin and levofloxacin (generic antibiotics present in clinical wastewater) as compared to neat mesostructured ZnO. Upscaling of the presented catalyst is straightforward promising high technical relevance.

Recovery and reuse of TiO2 photocatalyst from aqueous suspension using plant based coagulant - A green approach

Separation of TiO2 from aqueous suspension is a major constraint in heterogeneous photocatalytic water treatment. As an alternative for existing less effective immobilization techniques, the application of plant based coagulant for the recovery and reuse of TiO2 was investigated for the first time. Aqueous extract derived from seeds of Strychnos potatorum was found to be an effective coagulant for the sedimentation of TiO2. Further, the potential for recovery and reuse of the sedimented photocatalysts TiO2, was investigated by photocatalytic degradation of rhodamine B and terephthalic acid tests. The photocatalytic degradation experiments with recovered catalyst obey pseudo first-order kinetics with enhanced photocatalytic activity than that of the pure TiO2. The investigation of recovered catalysts with XRD, BET, SEM etc., suggests that there is no change in surface and morphological properties when compared with pure TiO2 and the recovered catalysts are highly suitable for recycle and reuse.

Heterogeneous Photocatalytic Treatment of Textile Effluent using Semiconductor Oxide under UV Irradiation

The present work deals with the photocatalytic degradation as a method for pre-treatment of the effluent from a textile industry containing various dyes and their intermediates which are non-biodegradable. The textile effluent was subjected to photocatalytic degradation under UV irradiation in the presence of TiO 2 as catalyst and the process parameters for maximum degradation were determined. Optimisation of catalyst dose and pH was carried out and the effect of addition of oxidant H 2 O 2 on the degradation efficiency was also studied. The effectiveness with which the photocatalyst can be recycled was also assessed to ensure the economic viability of the process.

Pharmaceutical Removal from Synthetic Wastewater Using Heterogeneous - Photocatalyst

Compound Parabolic Collecting Reactor (CPCR) was designed and used for the heterogeneous-photocatalytic treatment process. Sunray was act as an economically and ecologically sensible light source. The photocatalytic degradation of paracetamol in the synthetic wastewater by using titanium dioxide (TiO2) was investigated. The experimental results show that the paracetamol removal rates were very high and nearly equal (97.2% to 99.7%) at pH 4-7 and TiO2 concentration of 0.5-1 g/L. This implies that the photocatalytic degradation rate of paracetamol is not affected by pH range in this study as the electrostatic interaction between the TiO2 and paracetamol is not able to be developed unless a wider range of pH is set. Furthermore, the concentration of TiO2 of 0.5 g/L is too high to treat the concentration of 10 mg/L of paracetamol. Further research is needed in order to identify the optimum pH condition and a suitable correlation of concentration between TiO2 and paracetamol. Finally, the results proved that the heterogeneous-photocatalyst treatment method which associated with the application of CPCR and solar energy is able to eliminate the paracetamol from the synthetic wastewater.

Photocatalytic Degradation of Real Textile Industrial Effluent under UV Light Catalyzed by Metal Oxide Nanoparticles

The domestic use and industrial activity, especially in developing countries, produce large amount of wastewater. This wastewater when disposed into natural channels may lead to high pollution risk. There are different methods for wastewater treatment one of them is Advanced Oxidation Processes (AOPs), still it has some limitations. The present work has been concentrated on the degradation of real textile industrial effluent named as Efluent1. The said Effluent1 was collected from textile industry from Echalkaranji; Maharashtra state was subjected to photocatalytic treatment using photocatalyst such as Degussa P-25 TiO2. Efluent1 was analyzed before and after the treatment for their physiochemical parameters like color, COD, TOC and presence of inorganic ions. Throughout the study it was observed that Degussa P-25 TiO2 effectively brought out the degradation of Effluent. Addition of optimum amount of H2O2 to the heterogeneous photocatalytic treatment was found to enhance the degradation of real textile effluents to a large extent. Hence, the photocatalytic degradation was found to be fruitful treatment for degradation of real textile industrial effluent as well as by adding oxidant the photocatalytic degradation has been enhanced.DOI: http://dx.doi.org/njst.v15i2.12124Nepal Journal of Science and Technology Vol. 15, No.2 (2014) 105-110

Supported Photocatalyst for Removal of Emerging Contaminants from Wastewater in a Continuous Packed-Bed Photoreactor Configuration

Water pollution from emerging contaminants (ECs) or emerging pollutants is an important environmental problem. Heterogeneous photocatalytic treatment, as advanced oxidation treatment of wastewater effluents, has been proposed to solve this problem. In this paper, a heterogeneous photocatalytic process was studied for emergent contaminants removal using paracetamol as a model contaminant molecule. TiO2 photocatalytic activity was evaluated using two photocatalytic reactor configurations: Photocatalyst solid suspension in wastewater in a stirred photoreactor and TiO2 supported on glass spheres (TGS) configuring a packed bed photoreactor. The surface morphology and texture of the TGS were monitored by scanning electron microscope (SEM). The influence of photocatalyst amount and wastewater pH were evaluated in the stirred photoreactor and the influence of wastewater flowrate was tested in the packed bed photoreactor, in order to obtain the optimal operation conditions. Moreover, results obtained were compared with those obtained from photolysis and adsorption studies, using the optimal operation conditions. Good photocatalytic activities have been observed and leads to the conclusion that the heterogeneous photocatalytic system in a packed bed is an effective method for removal of emerging pollutants.

Recent developments in heterogeneous photocatalytic water treatment using visible light-responsive photocatalysts: a review

This review summarizes the recent progress in the design, fabrication, and application of visible light-responsive photocatalysts.

Graphene/semiconductor nanocomposites (GSNs) for heterogeneous photocatalytic decolorization of wastewaters contaminated with synthetic dyes: A review

The advent of graphene revolution in recent years has opened up immense possibilities for creating and exploring new carbon-based materials for innovative technological applications. Recent advancements have shown that graphene/semiconductor nanocomposites (GSNs) can be envisaged as a promising new class of catalysts for the heterogeneous photocatalytic treatment of industrial wastewaters. While GSNs have been found effective in degrading and mineralizing a myriad of organic contaminants, photocatalytic degradation of synthetic colorants has been most extensively investigated. We present here the state-of-art review on GSNs in the context of photodecolorization of textile effluents. Various approaches to the synthesis of GSNs are first integrated and demonstrated by representative examples. The efficacy of these composite photocatalysts in decomposing selected dye pollutants is then discussed. We conclude the review by emphasizing the future research challenges and opportunities toward the large-scale commercialization of GSNs.

Heterogeneous photocatalytic treatment of pharmaceutical micropollutants: Effects of wastewater effluent matrix and catalyst modifications

This study evaluates the applicability of TiO2-based photocatalysts for the treatment of pharmaceutical micropollutants in secondary wastewater effluent (SWE). Photolytic experiments using SWEs with different compositions demonstrated that the rates of photocatalytic degradation of acetaminophen and carbamazepine inversely correlated with the concentration of dissolved organic carbon (DOC), regardless of the type of applied light source and initial pharmaceutical concentration. The critical relevance of organic matter to the scavenging behavior of SWE was further verified by assessing the photocatalytic performance as a function of the concentrations of potential effluent-derived quenchers (i.e., NO3−, Cl−, alkalinity, and humic acid). Kinetic comparison of the degradation of trace levels of pharmaceuticals (i.e., caffeine, cimetidine, propranolol, and sulfamethoxazole) using TiO2/UV-A, TiO2/UV-C, and H2O2/UV-C systems revealed that heterogeneous processes showed more significant performance reduction with increasing DOC concentration; this result indicates that organic matter plays dual roles in the scavenging activity of an effluent matrix: (1) OH radical (OH) quenching and (2) active-site coverage. TiO2 surface modifications (i.e., Pt and SiOx loading) accelerated the degradation of all the tested pharmaceuticals in SWEs to a certain degree. Particularly, the relevant altered surface affinity preferentially increased the susceptibility of specific pharmaceuticals to photocatalytic treatment. The presence of the effluent matrix substantially impaired the performance of visible-light-active photocatalysts in most cases. However, photocatalytic pharmaceutical degradation on Pt-doped TiO2, which occurs via direct charge transfer, was much less hindered in SWEs than that on Pt-deposited WO3, which occurs via OH-mediated oxidation.

Heterogeneous photocatalytic treatment of wastewater in ultraviolet light irradiation—photocatalyst Bi2WO6 microsphere with high repeatability

The treatment of wastewater that includes toxic organic pollutants such as dyes, phenoaniline, phenols and their derivatives is still a challenge due to their biorecalcitrant and acute toxicity to the widespread acceptance of water recycling. Three-dimensional (3D) Bi2WO6 microsphere was synthesized by the hydrothermal method using Bi(NO3)3 and Na2WO4 as raw materials. This structure exhibits high photocatalytic activity for the dyes, toxic organic compounds. The degradation of methlyene blue is 100% in 30 min, 4-nitrylphenol is 95% in 60 min and p-nitrylphenol is 95% in 75 min in ultraviolet (UV) light irradiation. 3D Bi2WO6 microsphere is also a good photocatalyst to treat the printing and dyeing sewage, and exhibits high repeatability. After being used the 20th time, Bi2WO6 still has high activity to degrade the printing and dyeing sewage, which is very important for a photocatalyst to be used in industry. This study will pave a new way to treat industry wastewater.

Heterogeneous Photocatalytic Degradation of Selected Organophosphate Pesticides: A Review

This review is an attempt to summarize the research carried out on heterogeneous photocatalytic treatment of selected organophosphates present invariably in shallow and ground water supplies. The basic principle of semiconductor-mediated photocatalytic process, experimental conditions used, optimization of the parameters affecting the efficiency, and degradation mechanism has been explained. The kinetics of organophosphate degradation and the analytical techniques for identification of intermediates have been reviewed. The by-products and intermediates formed along with the proposed pathways for the degradation of various subclasses of organophosphate pesticides are widely discussed.

Decomposition of perfluorocarboxylic acids (PFCAs) by heterogeneous photocatalysis in acidic aqueous medium

Decomposition of perfluorocarboxylic acids (PFCAs) is of prime importance since they are recognized as persistent organic pollutants and are widespread in the environment. PFCAs with longer carbon chain length are particularly of interest because of their noted recalcitrance, toxicity, and bioaccumulation. Here in this study, we demonstrate efficient decomposition of three important PFCAs such as perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA) by heterogeneous photocatalysis with TiO 2 as a photocatalyst in acidic aqueous solutions. The PFCAs were decomposed into shorter carbon chain length PFCAs and fluoride ions. Photoholes of excited TiO 2 generated upon UV-irradiation are found to be the oxidation sites for PFCAs. Therefore, creation and sustenance of these photoholes in the acidic aqueous medium has enhanced the decomposition of PFCAs. Heterogeneous photocatalytic treatment achieved more than 99% decomposition and 38% complete mineralization of PFOA in 7 h. The decomposition of other PFCAs was as high as 99% with a defluorination efficiency of 38% for PFDA and 54% for PFNA. The presence of perchloric acid was found to enhance the decomposition by facilitating the ionization of PFCAs. The oxygen present in the medium served both as an oxidant and an electron acceptor. The mechanistic details of PFCA decomposition and their corresponding mineralization are elaborated.

Photodegradation of methyl green using visible irradiation in ZnO suspensions: Determination of the reaction pathway and identification of intermediates by a high-performance liquid chromatography–photodiode array-electrospray ionization-mass spectrometry method

Heterogeneous photocatalytic treatment of a dye called methyl green (MG), which was simulating textile wastewater from associated auxiliary chemicals, was investigated using ZnO. A detailed investigation of the photodegradation of MG has been carried out in the ZnO suspension irradiated with visible light. The effects of various factors – viz. pH values, amount of catalyst, initial dye concentration, and the presence of NaCl, Na 2CO 3, H 2O 2, and Na 2S 2O 8 – on the degradation efficiency were studied. Thirty-two intermediates were separated, identified, and characterized by high-performance liquid chromatography–photodiode array-electrospray ionization-mass spectrometry (HPLC–ESI-DAD-MS) technology, giving us insight into the pathways of the degradation process.

Photocatalytic degradation of paraquat and genotoxicity of its intermediate products

The photocatalytic degradation of paraquat (1,1-dimethyl-4,4′-bipyridylium dichloride) aqueous solutions in the presence of polycrystalline TiO 2 Degussa P25 irradiated by near-UV light was investigated. The substrate and total organic carbon concentrations were monitored by UV spectroscopy and TOC measurements, respectively: the complete photocatalytic mineralization of paraquat (20 ppm) was achieved after ca. 3 h of irradiation by using 0.4 g l −1 of catalyst amount at natural pH (ca 5.8). On the contrary no significant photodegradation of paraquat was observed in the absence of TiO 2 under similar experimental conditions. To evaluate the genotoxicity of paraquat and its intermediates produced during heterogeneous photocatalytic treatment, in vitro tests such as Ames test, with and without rat liver microsomal fractions (S9 mix), and micronucleus test, were used. Results obtained with Salmonella typhimurium (strain TA100) showed that paraquat and photocatalytic products were unable to induce gene mutations when photocatalysis was used in the presence of the optimum amount of TiO 2, i.e. 0.4 g l −1, whereas an increase of revertants his + per plate was observed after 300 min irradiation in the presence of very low amount of TiO 2 (0.04 g l −1). The negative results from micronucleus test suggest that mutagenic, but non-clastogenic, late intermediates of paraquat photo-oxidation were formed when the photocatalytic runs of paraquat degradation were carried out by using 0.04 g l −1 of photocatalyst.

Degradation of a commercial textile biocide with advanced oxidation processes and ozone

The occurrence of significant amounts of biocidal finishing agents in the environment as a consequence of intensive textile finishing activities has become a subject of major public health concern and scientific interest only recently. In the present study, the treatment efficiency of selected, well-known advanced oxidation processes (Fenton, Photo-Fenton, TiO 2/UV-A, TiO 2/UV-A/H 2O 2) and ozone was compared for the degradation and detoxification of a commercial textile biocide formulation containing a 2,4,4′-trichloro-2′-hydroxydiphenyl ether as the active ingredient. The aqueous biocide solution was prepared to mimic typical effluent originating from the antimicrobial finishing operation (BOD 5,o⩽5 mg/L; COD o=200 mg/L; DOC o (dissolved organic carbon)=58 mg/L; AOX o (adsorbable organic halogens)=48 mg/L; LC 50,o (lethal concentration causing 50% death or immobilization in Daphnia magna)=8% v/v). Ozonation experiments were conducted at different ozone doses (500–900 mg/h) and initial pH (7–12) to assess the effect of ozonation on degradation (COD, DOC removal), dearomatization (UV 280 and UV 254 abatement), dechlorination (AOX removal) and detoxification (changes in LC 50). For the Fenton experiments, the effect of varying ferrous iron catalyst concentrations and UV-A light irradiation (the Photo-Fenton process) was examined. In the heterogenous photocatalytic experiments, Degussa P25-type TiO 2 was used as the catalyst and the effect of reaction pH (3, 7 and 12) and H 2O 2 addition on the photocatalytic treatment efficiency was examined. Although in the photochemical (i.e. Photo-Fenton, TiO 2/UV-A and TiO 2/UV-A/H 2O 2) experiments appreciably higher COD and DOC removal efficiencies were obtained, ozonation appeared to be equally effective to achieve dearomatization (UV 280 abatement) at all studied reaction pH. During ozonation of the textile biocide effluent, AOX abatement proceeded significantly faster than dearomatization and was complete after 20 min ozonation (267 mg O 3). On the other hand, for complete detoxification, ozonation had to be continued for at least 30 min (corresponding to 400 mg O 3). Effective AOX and acute toxicity removal was also obtained after heterogeneous photocatalytic treatment (TiO 2/UV-A and TiO 2/UV-A/H 2O 2). The Fenton-based treatment experiments and particularly the dark Fenton reaction resulted in relatively poor degradation, dearomatization, AOX and acute toxicity removals.

TiO2-Based Heterogeneous Photocatalytic Water Treatment Combined with Ozonation

ABSTRACT The degradations of aliphatic carboxylic acids (formic acid, acetic acid, and propionic acid) were investigated by a combination of TiO2-based photocatalysis and ozonation at pH = 2. The carboxylic acids were analyzed by high-performance liquid chromatography (HPLC), while the mineralization process was characterized by measuring the dissolved organic carbon (DOC) content. The efficiency of heterogeneous photocatalysis combined with ozonation was compared with that of ozonation and that of heterogeneous photocatalysis alone. In all cases, the combined system proved most effective in the oxidation of carboxylic acids. The degradation of carboxylic acids was accompanied by a continuous decrease in the DOC content, and aldehydes and carboxylic acids containing one carbon atom less than the starting material were formed as intermediates.