Showing papers in "Journal of Photochemistry and Photobiology A-chemistry in 2017"

Photocatalytic efficiencies of Ni, Mn, Fe and Ag doped ZnO nanostructures synthesized by hydrothermal method: The synergistic/antagonistic effect between ZnO and metals

Abstract: The ZnO and different noble and transition metals (Ni, Mn, Fe and Ag) doped ZnO (M/ZnO) nanostructures were synthesized by hydrothermal method. The ZnO and M/ZnO photocatalysts were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), fourier transform infrared (FTIR) and UV–vis spectrophotometry. The obtained XRD and FESEM results confirmed the well dispersion of Ni and Ag nanoparticles and highly agglomerated Mn and Fe nanoparticles on the surface of ZnO nanostructures. The optical band gap value was calculated as 3.24, 3.15, 3.10, 3.05 and 3.00 eV from UV–vis diffuse reflectance spectra of ZnO, Ag/ZnO, Ni/ZnO, Fe/ZnO and Mn/ZnO photocatalysts, respectively. The results of the photocatalytic degradation of tartrazine in aqueous solutions under the UV-light showed that Ni/ZnO exhibited higher photocatalytic activity than the other ones. Mn/ZnO demonstrated the lowest photocatalytic activity among the synthesized photocatalysts. Thus, Ni and Ag exhibited synergistic effect while Fe and Mn exhibited antagonistic effect on the ZnO photocatalytic activity. The maximum degradation rate of tartrazine was obtained to be 98.2% in the 60 min using Ni/ZnO. The plausible mechanisms were proposed and discussed for the enhanced or decreased photocatalytic activities resulting from different metals doped ZnO.

Facile hetero-assembly of superparamagnetic Fe3O4/BiVO4 stacked on biochar for solar photo-degradation of methyl paraben and pesticide removal from soil

Abstract: Herein we report synthesis of nano-hetero assembly of superparamagnetic Fe 3 O 4 and bismuth vanadate stacked on Pinus roxburghii derived biochar. Optical studies and band structure analysis indicate the hybridization between the two semiconductors facilitating photodegradation of pollutants in presence of natural sunlight. The nano-heterojunctions have been utilized for removal of emerging micro-pollutants as methylparaben (MeP). 97.4% of MeP degradation was achieved in presence of biochar/Fe 3 O 4 /BiVO 4 in 2 h. A degradation pathway has also been proposed on basis of mass spectrometry, chemical oxygen demand analysis and effects of various scavengers. Pinus derived biochar has also been utilized to see its long term effect on soil characteristics and fertility. The biochar has also been used to remove excessive pesticide from soil for lesser bioavailability.

Visible active N, S co-doped TiO2/graphene photocatalysts for the degradation of hazardous dyes

Abstract: Herein, we report the synthesis of nitrogen and sulphur co-doped TiO2/rGO nano composites (NST/x%-rGO, x = 2.5, 5, 7.5 & 10%) by facile single step hydrothermal method. The structural and morphological analyses of the synthesized composites were made by XRD, IR, XPS, SEM and TEM, while optical properties were studied by Raman and DRS-UV spectrophotometric techniques. Charge separation efficiency and the extent of recombination were investigated by EIS and photoluminescence (PL) studies. Photodegradation efficiency was evaluated by the de-colorization of congo red (CR), methylene blue (MB) and reactive orange 16 (RO16) dyes. For comparison purpose, TiO2/rGO (GT) and nitrogen, sulphur co-doped TiO2 (NST) were also synthesized, characterized and their photocatalytic activities were evaluated and compared. NST/5%-rGO exhibited the highest photocatalytic activity towards the degradation of all the three dyes under visible light. Improved optical absorption property and increased life time of the photogenerated charge carriers have been observed. Trapping experiments with different quenchers suggested that superoxide radicals (O2 −) were highly responsible for the degradation process compared to other species such as hydroxyl radicals (OH ) and photogenerated holes (h+).

A comparison of graphitic carbon nitrides synthesized from different precursors through pyrolysis

Abstract: Two precursors, melamine and urea, were used to prepare graphitic carbon nitride through a thermal decomposition (pyrolysis) method. The pyrolysis was carried out at different temperatures in open air condition in a crucible with cover. The as-prepared samples were characterized by SEM, TEM, BET, XRD, XPS, FTIR and DRS. The characterization results revealed that the samples synthesized from different precursors had different physical and chemical properties. Specifically, it was found that the pyrolysis of urea yielded product with smaller crystalline domains but larger surface areas compared to that of melamine. To further qualify the as-prepared samples, the adsorption and photocatalytic activities were measured by using Rhodamine B (RhB) as target pollutant. It was found out that the precursors as well as pyrolysis temperatures had big influences on the adsorption and photocatalytic activities. Higher photocatalytic activities were achieved by samples synthesized from urea at higher temperatures. The mechanism of the degradation process was explored on the basis of the band structure and the roles of photo-generated radicals.

Effective photocatalytic degradation of anthropogenic dyes using graphene oxide grafting titanium dioxide nanoparticles under UV-light irradiation

Abstract: Graphene oxide grafting titanium dioxide nanoparticles (TiO 2 -GO nanocomposite) was successfully synthesized by a simple solvothermal method. The synthesized TiO 2 -GO nanocomposite were systematically characterized by various physico-chemical techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The XRD results confirm the crystallinity of synthesized bare titanium dioxide nanoparticles (TiO 2 NPs), pristine graphene oxide (GO) and TiO 2 -GO nanocomposite with high pure in nature. The average size of the bare TiO 2 NPs was around 5 nm and were dispersed over the wrinkled graphene layers. Raman spectrum shows the resulting GO and TiO 2 -GO nanocomposite exhibit moderate graphitization with the intensity of D to G value was 1.1 and 1.2, respectively. The chemical state, functionality and composition (carbon, oxygen and titanium) of the resulting TiO 2 -GO nanocomposite were revealed by XPS analysis. The photocatalytic activity of synthesized TiO 2 -GO nanocomposite was investigated on the degradation of hazardous organic dyes (methylene blue (MB) and methyl orange (MO)) under UV-light irradiation and was compared with bare TiO 2 NPs and were presented based on the preferred propagation path of induced electrons that leads to generation of O 2 ─ . The resulting TiO 2 -GO nanocomposite achieve a maximum degradation efficiency of 100 and 84% on MB and MO in a neutral solution within 25 and 240 min, respectively under UV-light irradiation, the results show that the GO plays an important role in the enhancement of photocatalytic performance. The high photocatalytic efficiency due to the increased light absorption, the reduced charge recombination with the introduction of GO. Moreover, the simple and affordable solvothermal derived TiO 2 -GO nanocomposite exhibit rapid photocatalytic degradation on MB in 25 min of UV-light irradiation.

Kinetic degradation of chloramphenicol in water by UV/persulfate system

Abstract: Performances of chloramphenicol (CAP) degradation by direct ultraviolet (UV) irradiation, persulfate (PS) oxidation alone and UV irradiation-activated persulfate process (UV/PS) were systematically studied. UV/PS oxidation was superior over direct UV irradiation or PS oxidation alone. Both SO 4 − and HO were existing in UV/PS system, and SO 4 − was proved to be the primary radical species through the scavenging tests. The secondary order reaction rate constant between CAP and SO 4 − was estimated to be 1.33 × 10 10 M −1 s −1 . The CAP degradation fitted the pseudo-first-order kinetics well (R 2 > 0.95) in tests. Higher PS dosage, lower initial CAP concentration and acid pH promoted the CAP degradation. A maximum TOC removal of 31.7% was observed in 120 min at conditions of [CAP] 0 = 0.03 mM and [PS] 0 = 1.0 mM. At last, the electrical energy per order (EE/O) value in system was demonstrated to be 16.76 kWh/m 3 /order. Results indicated that the UV/PS system is potential alternative to control water pollution caused by emerging contaminants such as CAP.

Effect of inorganic ions, photosensitisers and scavengers on the photocatalytic degradation of nicosulfuron

Abstract: In the present study, the photocatalytic degradation of nicosulfuron, using TiO 2 as a catalyst under UV light (315–400 nm), was studied. The optimization of the nicosulfuron photodegradation was performed. It was found that the optimal concentration of the catalyst was 1 g L −1 at concentration of nicosulfuron solution of 20 mg L −1 while the highest reaction rate was obtained using 2 g L −1 . The degradation rate was the highest at pH = 5.0. Effects of anions (Cl − , SO 4 2– , NO 3 − and F − ) and cations (Na + , Ca 2+ , Al 3+ ) were investigated. In addition, the influence of isopropanol, acetone, and hydrogen peroxide was studied. It was shown that the photocatalytic degradation is mainly due to the reaction of nicosulfuron with OH in solution. Also, liquid chromatography coupled with mass spectrometry (HPLC–MS) was used to identify intermediates during the photocatalytic degradation of nicosulfuron. the mineralization was monitored with ion chromatography (IC) and total organic carbon (TOC) analysis. Although 100% HPLC removal of nicosulfuron was achieved, only 69% TOC removal after 90 min was recorded. The results of ion chromatography showed that the mineralization resulted in ammonium and nitrate ions during the process. The phytotoxicity experiments using mung bean seeds showed a reduction in phytotoxicity.

Photocatalytic degradation of paracetamol over magnetic flower-like TiO2/Fe2O3 core-shell nanostructures

Abstract: The presence of pharmaceutical residues and their metabolites in water, even in low concentrations, is of significant concern due to their effects on aquatic environment. The application of new recyclable photocatalysts with high photocatalytic activity and stability for water treatment has received increasing attention in recent times. In this work, photocatalytic degradation of paracetamol (PA) has been investigated in aqueous solution over magnetically separable flower-like TiO 2 /Fe 2 O 3 core-shell photocatalysts using 450 W medium pressure mercury lamp. SEM, TEM, N 2 sorption (BET method), XRD, FTIR, Raman spectroscopy and VSM were used to characterize the prepared photocatalysts. Results showed that photodegradation and photomineralization of paracetamol was increased with increasing TiO 2 content in the TiO 2 /Fe 2 O 3 core-shell. GC and GC/MS were used to identify the intermediate products formed during the degradation of paracetamol. 4-Acetamidoresorcinol, 4-acetamidocatechol, hydroquinone, 1,2,4-benzenetriol in addition to aliphatic acids were identified in the photolysate mixture. The 33%TiO 2 /Fe 2 O 3 core-shell photocatalyst showed high photoctalaytic efficiency for the degradation of paracetamol after four repeated cycles which demonstrates the high stability of the prepared photocatalyst. A pseudo first order rate was demonstrated for the photocatalytic degradation process of paracetamol.

Multi-functional properties of ternary CeO2/SnO2/rGO nanocomposites: Visible light driven photocatalyst and heavy metal removal

Abstract: An eco-friendly ternary CeO2/SnO2/rGO (CSG) nanostructured photocatalyst was successfully synthesized via hydrothermal process. The nanocomposites material was characterized various analytical techniques such as X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and thermogravimetric analysis (TGA). The synthesized CSG nanocomposites were used to remove methylene blue (MB) as a model organic pollution under solar light irradiation. The MB removal efficiency of CSG was found 95% for 90 min, which is showing synergy between binary composites CeO2/rGO and SnO2/rGO. The enhanced photocatalytic system is described in terms of increased light absorption intensity, reduced bandgap which enable the electron transfer, scavengers of the reactive species and prolonged photogenerated charge carriers. Also, this material was used to remove heavy metal ions (Pb2+ and Cd2+) in wastewater via batch equilibrium method have been studied. Unexpectedly, CSG nanocomposites was used photocatalyst against bacterial growth (gram-negative E. coli and gram-positive S. aureus) in aqueous solution. The synthesized catalyst having capability for enhance photoactive nanocomposites open up a new opportunities in various areas in photocatalysis.

Efficiently enhancing photocatalytic activity of NiO-ZnO doped onto nanozeoliteX by synergistic effects of p-n heterojunction, supporting and zeolite nanoparticles in photo-degradation of Eriochrome Black T and Methyl Orange

Abstract: The goal of this work is to use the photo-catalyst NiO-ZnO doped onto nano zeolite X (NZX) with a p-n heterojunction semiconductor structure in the photo-catalytic degradation of Eriochrome Black T (EBT) and Methyl Orange (MO) under UV-light irradiation Nano-zeolite crystals were synthesized by hydrothermal crystallization Ion exchanging of the prepared Nano zeolite in an aqueous solution containing Ni(II) and Zn(II) cations and calcinations of the ion-exchanged material at 450 °C led to the formation of NiO-ZnO-NZX catalyst The samples were characterized by XRD, UV/vis-DRS, FT-IR, TEM and BET The composites exhibited significantly enhanced photo-degradation activity for the degradation of (EBT) and (MO) A synergistic effect of mixed p–type NiO and n–type ZnO oxides incorporated in NZX has been noticed on the photo-degradation process Several influencing process parameters, such as the NiO-ZnO ratio, pH, initial dyes concentrations, dosage of photo-catalyst, were also investigated The extent of degradation was estimated from the residual concentration by spectrophotometrically and it was confirmed by the reduction of chemical oxygen demand (COD)

Novel TiO2/Ag2CrO4 nanocomposites: Efficient visible-light-driven photocatalysts with n–n heterojunctions

Abstract: In this study, novel TiO 2 /Ag 2 CrO 4 nanocomposites were fabricated by a facile refluxing method using commercial TiO 2 , silver nitrate, and sodium chromate at low temperature of 96 °C. The as-prepared photocatalysts were characterized by XRD, EDX, SEM, TEM, UV–vis DRS, FT–IR, BET, and PL techniques. Compared with the TiO 2 sample, TiO 2 /Ag 2 CrO 4 nanocomposites exhibited highly enhanced photocatalytic activity in degradations of rhodamine B (RhB), methylene blue (MB), and fuchsine dyes under visible-light irradiation. Among the prepared photocatalysts, the TiO 2 /Ag 2 CrO 4 (50%) nanocomposite showed the superior activity of 8.8, 5.4, and 44-folds relative to the TiO 2 sample in degradations of RhB, MB, and fuchsine, respectively. The trapping experiments demonstrated that holes and superoxide anion radicals were the main reactive species in the degradation reaction. Based on the obtained results, the photocatalytic activity enhancement was attributed to strong visible-light absorption, effective separation of photogenerated charge carriers by internal electrostatic field produced through n–n heterojunction formed between counterparts of the nanocomposite, and enhanced surface area.

Microwave assisted fabrication of La/Cu/Zr/carbon dots trimetallic nanocomposites with their adsorptional vs photocatalytic efficiency for remediation of persistent organic pollutants

Abstract: Herein we report a greener microwave method for fabrication of La/Cu/Zr/carbon quantum dots trimetallic nanocomposites(La/Cu/Zr/CQDs TNCs). The structural aspects and chemical nature of the TNCs were considered using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The optical band property of the trimetallic nanocomposites was examined using UV–vis spectroscopy. The adsorptional versus photocatalytic activity of the La/Cu/Zr/CQDs TNCs was investigated for the removal of a persistent organic pollutant i.e., malachite green dye and ampicillin antibiotic, under visible light irradiation. Overall, the current approach relates to green chemistry principles for fabrication La/Cu/Zr/CQDs trimetallic nanocomposites which hold promise for the development of surprisingly proficient adsorptional-photocatalytic systems. It has been observed that 96% ampicillin antibiotic and 86% of malachite green were degraded in 4 h of photoirridation under adsorption in dark followed by photocatalysis and coupled adsorptional/photocatalysis process.

Precipitation dispersion of various ratios of BiOI/BiOCl nanocomposite over g-C3N4 for promoted visible light nanophotocatalyst used in removal of acid orange 7 from water

Abstract: BiOI-BiOCl/g-C3N4 composite photocatalysts with different weight percentages of BiOI and BiOCl were synthesized by a facile precipitation method at room temperature. The synthesized composites were well characterized by XRD, EDX, FTIR, TEM, BET, FESEM and UV–vis DRS techniques. The results indicated that the successful combination of three components greatly enhanced visible light absorption. Among prepared samples, the BiOI(50)-BiOCl(30)/C3N4(20) composite exhibited superior photocatalytic activity for degradation of acid orange 7 under visible light irradiation. The degradation efficiency was found to be 97.4% for this composite. Also, surface ionization behaviour of photocatalyst was investigated and the pHPZC of the BiOI(50)-BiOCl(30)/C3N4(20) was found to be 6. The increased photocatalytic activity of this composite is mainly attributed to the efficient separation and transfer of photogenerated electron-hole pairs originating from the formation of multi-heterojunction structure between BiOCl, BiOI and g-C3N4. To find the optimum condition for photocatalysis, the effects of pH, photocatalyst loading, initial concentration of the model contaminant were investigated. Also, photostability of BiOI(50)-BiOCl(30)/C3N4(20) was examined and possible photocatalytic mechanism for degradation of acid orange 7 was proposed.

Direct solvothermal synthesis of zinc oxide nanoparticle decorated graphene oxide nanocomposite for efficient photodegradation of azo-dyes

Abstract: Zinc oxide nanoparticles decorated graphene oxide (ZnO@GO) nanocomposite was successfully prepared using graphene oxide (GO) and zinc oxide nanoparticles (ZnO NPs) as raw materials by simple solvothermal method. The X-ray diffraction pattern, X-ray photoelectron spectroscopic, Fourier transform infrared spectroscopic, and Raman spectroscopic techniques revealed the formation, elemental composition and the purity of ZnO NPs and ZnO@GO nanocomposite. The ZnO NPs were synthesized via simple thermal oxidation, the synthesized ZnO NPs exhibits an excellent near spherical shape with narrow size distribution and mean size of around 20 ± 5 nm which is vividly observed from field emission scanning electron microscopic images. The elemental compositions of ZnO@GO nanocomposite which carbon, oxygen and zinc were revealed by XPS and EDX elemental mapping. The ZnO NPs decorated on GO layers were clearly seen in the high resolution transmission electron microscopic images. The photocatalytic activities of the synthesized pure ZnO NPs and ZnO@GO nanocomposite were investigated by photodegradation of azo-dyes includes neutral red (NR), crystal violet (CV), congo red (CR) and methyl orange (MO) under UV-light irradiation. The results revealed that the ZnO@GO nanocomposite exhibited a remarkably higher photocatalytic efficiency compared to pure ZnO NPs. The enhancement of photocatalytic performance was ascribed to the synergistic effect between ZnO NPs and GO layers. Hence, the synthesized ZnO@GO nanocomposite crucial for efficient degradation of dyes such as NR, CV, CR and MO. The synthesized ZnO@GO nanocomposite exhibits a good photocatalytic activity along with good reproducibility of photodegradation, which is applicable for practical applications.

Development of multifunctional self-cleaning and UV blocking cotton fabric with modification of photoactive ZnO coating via microwave method

Abstract: A new self-cleaning cotton fabric coated with zinc oxide (ZnO) was obtained via a facile and effective microwave method. The solution pH was a key factor in determining the morphology of ZnO crystal growth on the cotton fibers: rod structures were apt to be formed at pH 4–5, whereas flake and flower-like structures were preferentially formed at higher solution pHs of 6–7 and 10–11, respectively. It is proved that the photocatalytic and wettability performances of ZnO could be efficiently transferred to cotton fabric, leading to a preeminent UV-blocking and self-cleaning cotton fabric. The identified UV protection factors (UPFs) indicate the excellent UV-blocking properties of the ZnO-coated textile fabric synthesized at pH 6–7, 8–9 and 10–11 with UPFs of 222.52, 162.68 and 202.57, respectively. The ZnO coating layer on the cotton fabric significantly improved the wetting behavior of the fabric, such as water absorption speed, thereby affording a self-cleaning ability for the ZnO-coated cotton fabrics. This ability was checked according to the removal degree of coffee stain under UV irradiation at different humidities (30–90% RH). The coffee stains on the ZnO-coated cotton fabrics were almost removed after 15 h without needing any water or detergent and the highest removal effect was observed at 90% humidity.

Photocatalytic degradation of Rhodamine B dye by cotton textile coated with SiO2-TiO2 and SiO2-TiO2-HY composites

Abstract: The authors thank CAPES from Brazil for the financial support of this work This work is also a result of project “AIProcMat@N2020 − Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020”, with the reference NORTE-01-0145-FEDER-000006 and the project BioTecNorte (operation NORTE-01-0145-FEDER-000004), supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF) This work also has been funded by ERDF through COMPETE2020 − Programa Operacional Competitividade e Internacionalizacao (POCI), Project POCI-01-0145-FEDER-006984 − Associate Laboratory LSRE-LCM and by national funds through FCT − Fundacao para a Ciencia e a Tecnologia for project PTDC/AAGTEC/5269/2014 and Centre of Chemistry (UID/QUI/00686/2013 and UID/QUI/0686/2016)

Comparative assessment of visible light and UV active photocatalysts by hydroxyl radical quantification

Abstract: A simple method for determining hydroxyl radical yields on semiconductor photocatalysts is highly desirable, especially when comparing different photocatalyst materials. This paper reports the screening of a selection of visible light active photocatalysts such as Pt-C3N4, 5% LaCr doped SrTiO3, Sr0.95Cr0.05TiO3 and Yellow TiO2 and compares them against WO3 and ultra violet (UV) light activated TiO2 P25 (standard commercial catalysts) based on their oxidative strengths (OH radical producing capability) using a well-studied chemical probe–coumarin. 7-hydroxycoumarin, the only fluorescent hydroxylation product of this reaction can then be measured to indirectly quantify the OH radicals produced. P25 under UV light produced the highest concentration of OH radicals (16.9 μM), followed by WO3 (0.56 μM) and Pt-C3N4 (0.25 μM). The maximum OH radical production rate for P25, WO3 and Pt-C3N4 were also determined and found to be 35.6 μM/hr, 0.28 μM/h and 0.88 μM/h respectively. The other visible light activated photocatalysts did not produce any OH radicals primarily as a result of their electronic structure. Furthermore, it was concluded that, if any visible light absorbing photocatalysts are to be fabricated in future for the purpose of photocatalytic oxidation, their OH radical producing rates (and quantities) should be determined and compared to P25.

A comprehensive study on enhancement and optimization of photocatalytic activity of ZnS and SnS2: Response Surface Methodology (RSM), n-n heterojunction, supporting and nanoparticles study

Abstract: SnS2-ZnS supported clinoptilolite nanoparticles (NC) were used in photodegradation of metronidazole (MZ). The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results agreed with the photodegradation results, so the coupled SnS2-ZnS-NC system with higher charge transfer ability than the monocomponent systems showed the best photodegradation activity. The simultaneous effects of the experimental parameters were optimized using response surface methodology (RSM), which suggests that the interaction of solution pH and irradiation time had the important role on the response. The best run includes pH 3, catalyst dose of 3 g L−1, 2 mg L−1 of MZ at irradiation time of 250 min. R2 of 0.9868 confirms that the data predicted by RSM well agree with the experimental results. Initial pH and CMZ have an antagonistic effect on the response, meaning that increasing their values decrease MZ photodegradation. During the photodegradation of MZ over the SnZS-NC catalyst, sharp decrease in the UV–vis absorption was happened for the peak at 321 nm, while the intensity of the absorption peak about 234 nm was increased, indicating that the nitro group and nitrogen existing in metronidazole was degraded and formed nitrite ion.

Carbon dots and Ag nanoparticles decorated g-C3N4 nanosheets for enhanced organic pollutants degradation under sunlight irradiation

Abstract: In this work, novel ternary composites were prepared by depositing both carbon dots (CDs) and Ag nanoparticles (AgNPs) onto the surface of g-C 3 N 4 nanosheets (CNNs). The as-prepared samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) techniques. The characterization results demonstrated that the CDs and AgNPs were well distributed on the surface of CNNs. The photocatalytic activities of all the samples were evaluated by degrading methyl orange (MO) and p-nitrophenol (PNP) in aqueous media under sunlight irradiation. Among the prepared samples, CNNs decorated with 2 wt% CDs and 1 wt% AgNPs showed higher degradation performance. The enhanced performance was attributed to the improved light harvesting capability and effective charge carrier separation at the AgNPs/CDs/CNNs interface. Superoxide radical species and photogenerated holes were found to be predominant reactive species responsible for the photodegradation of these pollutants. A suitable mechanism was proposed and discussed in detail.

Triclosan degradation by heterogeneous photocatalysis using ZnO immobilized in biopolymer as catalyst

Abstract: Triclosan (TCS) is compound with bactericidal effect that is frequently used in personal care products. Classified as an emerging contaminant, TCS is found in the environment at low concentrations and it is difficult to degrade by conventional water treatment processes. For this reason, the objective of this work is to evaluate the capacity of heterogeneous photocatalysis in the triclosan degradation using zinc oxide (ZnO) immobilized in sodium alginate. A complete characterization of the free and immobilized forms of ZnO was performed, and its crystalline phase was identified as wurtzite. The determined bandgaps of free and immobilized ZnO were 3.14 eV and 3.08 eV respectively, involving no change in the bandgap potential of the semiconductor. High efficiency of TCS degradation was obtained (greater than 90%) using free and immobilized catalyst in only 20 min of reaction. These results showed that the immobilized semiconductor has practically the same performance as the free form. In addition, studies of degradation were carried out using solar radiation and immobilized semiconductors. In these conditions, high rates of degradation were observed (90% in 90 min). The utilization of ZnO immobilized in biopolymer and solar radiation can be an interesting alternative since the use of biodegradable support and alternative energy sources is very attractive from an environmental perspective.

Facile fabrication of direct Z-scheme MoS2/Bi2WO6 heterojunction photocatalyst with superior photocatalytic performance under visible light irradiation

Abstract: Direct Z-scheme photocatalyst systems with efficient charge separation as well as outstanding oxidation and reduction ability have been under immense investigation. In our work, direct Z-scheme MoS 2 /Bi 2 WO 6 heterojunctions were prepared by a facile method. The heterostructure was formed by loading MoS 2 nanoparticles on the surface of Bi 2 WO 6 nanosheets. It was found that the as-prepared MoS 2 /Bi 2 WO 6 composites showed superior photocatalytic activity than that of individual MoS 2 and Bi 2 WO 6 . The optimal composite with 4 at% MoS 2 content exhibited the highest photocatalytic activity. Based on the active species trapping experiments, photoluminescence spectroscopy analysis, and photocurrent responses, the possible enhanced photocatalytic mechanism could be ascribed to a direct Z-scheme heterojunction system which can not only increase the separation efficiency of photogenerated electron-hole pairs but also possess a splendid oxidation and reduction ability for high photocatalytic performances. This work provides an effective approach to develop other Bi 2 WO 6 -based direct Z-scheme photocatalytic systems for environmental purification and energy conversion.

ZnO nanotubes: Preparation and photocatalytic performance evaluation

Abstract: In this work, uniform zinc oxide nanotube was successfully synthesized by a simple reproducible solution-based method. The effects of temperature, molecular weight of polyethylene glycol, and synthesis time on morphology and photocatalytic properties of the products were investigated. The synthesized particles were characterized by X-ray diffraction, electron microscopy, laser particle sizing, thermal gravimetric analysis, differential scanning calorimetry, and photoluminescence spectrum. The reaction temperature and reaction time were found to play key roles in synthesis of the nanotubes. The effects of annealing on crystallinity, optical property, and photocatalytic activity of the nanotubes were also investigated. The photocatalytic activity of nanotubes was evaluated by degrading Acid Blue 9 as a pollutant dye in a slurry reactor under UV light. The photocatalytic activity of the synthesized ZnO nanotube remains almost unchanged after three times reusing that indicates its improved stability compared to that of a commercial ZnO nanoparticle.

Highly active non-metals doped mixed-phase TiO2 for photocatalytic oxidation of ibuprofen under visible light

Abstract: Visible light-activated C, N, S-tri-doped mesoporous anatase-brookite heterojunction TiO2 photocatalyst has been synthesized by a facile hydrothermal method. The XRD and Raman spectra data revealed the formation of mixed anatase and brookite phases. The FE-SEM and TEM images demonstrated the formation of brookite phase with a rod-like structure composed of much smaller particles of anatase phase. N2 isotherm measurements exhibited that both doped and undoped TiO2 have mesoporous structure and their surface area measurements were reduced from 62 to 30 cm2 g−1after non-metals doping. The photocatalytic oxidation of the ibuprofen (IBF) has been evaluated using prepared photocatalysts under visible light. The photocatalytic activity of the mesoporous C, N and S co-doped TiO2 photocatalyst dramatically increased, achieving complete IBF degradation with an initial 1st order rate 1.779 μM min−1 for 5 h. The photonic efficiency (ξ) of IBF degradation under visible light with ABH (un-doped) and DABH (doped) photocatalysts are 0.044% and 1.84%, respectively. The reaction rate of doped photocatalyst is greater 40 times than non-doped one. The results demonstrated the advantages of the synthetic approach and the great potential of the driven visible light C, N and S co-doped TiO2 photocatalysts for the treatment of residual pharmaceuticals in contaminated water under visible light.

Facile approach for homogeneous dispersion of metallic silver nanoparticles on the surface of mesoporous titania for photocatalytic degradation of methylene blue and indigo carmine dyes

Abstract: Homogeneous incorporation of an appropriate amount of metallic Ag nanoparticles on titania surface is essential parameter in optimizing the photocatalytic reactivity and stability of the photocatalyst. In this current research, metallic silver nanoparticles decorated titania were synthesized by sol-gel route using chitosan as nano-assembling template and reducing agent. The physicochemical features were investigated by X-ray diffraction [XRD], N 2 -adorption-desorption isotherm, Energy dispersive X-ray [EDX], diffuse reflectance spectra (DRS), Photoluminescence [PL], Field emission Scanning emission electron microscope [FESEM] and High resolution transmission electron microscope. Three prevailing diffraction peaks in XRD analysis assigned to metallic silver nanoparticles was observed confirming the successful role of chitosan in reducing silver ions. Various pores of different sizes ranging from supermicropores to wide mesoporous structure are created due to deposition of Ag particles on titania pore mouth. Benefiting from the uniform dispersion of Ag nanoparticles, the Ag/TiO 2 nanohybrids show favorable reactivity in the photodegradation of methylene blue and indigo carmine dye as cationic and anionic pollutant models. This enhanced photocatalytic reactivity arise from the positive synergetic effects of the metallic silver nanoparticles and titania including an electron transfer from titania conduction band to fermi level of metallic silver nanoparticles and reduction in electron-hole recombination. This novel research work will open a new doorway to prepare highly photoactive mesoporous Ag/TiO 2 nanoparticles without using an external reducing agent.

High luminescent carbon dots as an eco-friendly fluorescence sensor for Cr(VI) determination in water and soil samples

Abstract: In this work were synthesized highly luminescent carbon dots for use as fluorescence sensor for Cr(VI). Carbon dots (CDots) were prepared by pyrolysis of the mixture of molecular precursors as citric acid and reduced glutathione. Pyrolysis revealed to be a simple procedure that afforded CDots with a photoluminescence quantum yield of 69.4%, and particle size of about 2.5 nm. To explore the analytical potentiality of the nanomaterial produced, the CDots were applied as fluorescent sensors to determine Cr(VI) in water and soil samples. The interaction mechanism between CDots and Cr(VI) is associated with both inner filter effect and static quenching. After optimization of the main analytical parameters, the method showed a linear range of 0.10–12 μg mL −1 with limit of detection (LOD) of 0.03 μg mL −1 (pH 7), and recoveries of 90–105% and 99.5–107% for samples of water and soil, respectively. Thus, the method proved to be sensitive, fast and versatile for applications in different environmental samples.

Efficient photocatalytic degradation of Safranin O by integrating solar-UV/TiO2/persulfate treatment: Implication of sulfate radical in the oxidation process and effect of various water matrix components

Abstract: In this work, the degradation of Safranin O (SO), a cationic dye pollutant, by integrating UV/TiO 2 /PPS treatment (PPS: potassium persulfate) was found to be more efficient than UV/TiO 2 and UV/PPS individual binary systems. The complete removal of SO by the integrated system was achieved after only 25 min, whereas 22, 39, 83 and 97% of SO remained in the solutions with UV/TiO 2 , UV/PPS, UV and PPS separated systems. Moreover, the combination of UV/TiO 2 and UV/PPS exhibited a synergistic effect. A complete systematic study of SO removal by UV/TiO 2 /PPS system was carried out by assessing the effect of operating parameters, additives and several complex matrices. Chemical probes experiments showed that both OH and SO 4 − radicals contribute efficiently in the degradation of the dye by the UV/TiO 2 /PPS system. It was found that the degradation of the dye did not obey first-order kinetics law. The initial degradation rate increased significantly with the increase of initial dye and PPS concentrations, catalyst loading, liquid temperature and solution pH. Salts such as KNO 3 and Na 2 CO 3 enhanced notably the degradation of the dye probably by the formation of secondary radicals, such as CO 3 − , NO 2 and NO 3 , which participate in the oxidation reactions. Humic acid, as natural organic matter, decreased the efficiency of the integrated process toward the removal of SO. The conversion yield of SO by the UV/TiO 2 /PPS process was improved when the experiments was performed in natural mineral water, making this process as a promising technique for treating contaminated real natural waters. However, the very high quantity of salts present in seawater alters the reaction of radicals with the dye molecules resulting in lower degradation rate.

Enhanced photocatalytic degradation of atenolol using graphene TiO2 composite

Abstract: Graphene oxide-TiO 2 (TiO 2 -G) composite synthesized by a facile route is able to exhibit significantly higher photocatalytic activity under visible light irradiation. The prepared composite was characterized by means of powder X-ray diffraction (XRD), Scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), UV–vis diffuse reflectance spectroscopy (DRS), and Brunauer Emmett Teller (BET). The photocatalytic activity was evaluated by photo-degradation of the Atenolol (ATL) as model pharmaceutical pollutant under UV–vis light and “simulated Sun” irradiation conditions. The results showed that TiO 2 -G exhibited much higher photocatalytic performance than that of bare TiO 2 . The enhanced activity can be ascribed to the incorporation of graphene. The effect of various factors such as variation of pH, catalyst concentration, initial substrate concentration, light intensity, and source of light as well as reaction kinetics were investigated. The results showed that 72% degradation of ATL (25 ppm) can be achieved with 1.5 g/L TiO 2 -G in 1 h under solar irradiation. Complete TOC removal for atenolol degradation was obtained in 7 h. The work is expected to shed new light on the development of graphene composite nanostructures for gathering visible light energy and on the improvement of new photocatalytic materials for the exclusion of environmental pollutants.

Mixed α-Fe2O3/Bi2WO6 oxides for photoassisted hetero-Fenton degradation of Methyl Orange and Phenol

Abstract: Mixed oxides, α-Fe2O3/Bi2WO6, were prepared using a mechanical mixing procedure by adding to the Bi2WO6 previously obtained by hydrothermal method the corresponding amount of a prepared α-Fe2O3, the latter obtained by thermal decomposition of Fe(NO3)∙9H2O. The physicochemical surface, structural, morphological characteristics and optical properties of the samples, single and mixed, were determined by BET, XRD, FE-SEM, XPS and UV–vis diffuse reflectance spectroscopy. UV–vis diffuse reflectance spectra showed that incorporating a 5%wt. of α-Fe2O3 to the corresponding amount of Bi2WO6 sample broadened the visible light absorption of Bi2WO6 as expected. The photocatalytic activity, of single and mixed catalysts, to degrade a selected dye such as Methyl Orange (MO) as well as the transparent substrate Phenol (Ph) was studied, in aqueous medium (pH ≈ 5.5) under UV and sun-like illumination conditions in the absence and presence of H2O2. In the present study the use of a α-Fe2O3-Bi2WO6/H2O2 system demonstrate much higher photocatalytic efficiency to degrade both MO and Ph than pristine Bi2WO6or α-Fe2O3, single or mixed. Using the system α-Fe2O3-Bi2WO6/H2O2, around 85% of MO was degraded in 60 min under sun-like illumination whereas 100% was degraded in 60 min under UV-illumination. However, just around 30% of Ph was degraded in 120 min in the α-Fe2O3-Bi2WO6/H2O2 system under sun-like illumination whereas around a 95% was degraded in 90 min under UV-illumination. Under UV-illumination, the generation of hydroxyl radicals is favorable; whereas under sun-like illumination, only the small fraction of the UV can produces the OH. Under illumination, the H2O2 could react with photoinduced electrons from the photocatalysts leading to the production of hydroxyl radicals ( OH).

Synergistic effect of dual process (photocatalysis and photo-Fenton) for the degradation of Cephalexin using TiO2 immobilized novel clay beads with waste fly ash/foundry sand

Abstract: Novel composite clay beads mixed with foundry sand (FS)/fly-ash (FA) were used as support materials for fixing the catalyst TiO 2 and subsequently used as iron source. The in-situ iron generation in case of beads that contained either FS/FA or both induced dual effect (photo-Fenton and photocatalysis) in the same treatment unit thus leading to synergistic effect for the degradation of antibiotic Cephalexin. Composite beads (FS/FA/TiO 2 ) showed relatively best results (89% degradation) as compared to FS/TiO 2 (79%) or FA/TiO 2 (81%) at optimized conditions. From the kinetics data, there was 30–45% increase in first order rate constant in case of FS/FA/TiO 2 beads pertaining to dual effect. The stability of the catalyst even after 35 recycles, as confirmed through SEM/EDS and XRD analysis; justified its claim for field-scale applications. Further, mineralization of pollutant was validated by reduction in COD (82%) along with generation of various anions whereas intermediate products were identified through GC–MS analysis.

Interfacial charge-transfer process across ZrO2-TiO2 heterojunction and its impact on photocatalytic activity

Abstract: In this paper, ZrO2-TiO2 composites were synthesized by sol-gel method with different ZrO2:TiO2 molar ratios (01:99, 05:95 and 10:90). The results identified two trends; at a low ZrO2 content, the incorporation of Zr4+ into the TiO2 lattice was possible provoking generation of oxygen vacancies (1 mol% of ZrO2); while at higher ZrO2 contents, ZrO2-TiO2 heterojunctions were created (5 and 10 mol% of ZrO2). The photocatalytic activity was evaluated by measuring photodegradation of phenoxyacetic acid, 2,4-dichlorophenoxyacetic acid or 4-chlorophenol solutions. The ZT-5 composite shows the best performance attributed to surface states at the interface of ZrO2-TiO2 heterojunctions. These surface states act as traps for charge carriers favoring the spatial separation of electron-hole pairs until reaching a maximum in the composite with 5 mol% of ZrO2. The ZT-5 composite showed the most negative flat band potential and the highest donor density indicating that these surface states are in optimal concentration. At higher ZrO2 contents, charge carrier separation is less effective, which decreases the photocatalytic activity. Nevertheless, the molecule structure has an impact on the direct or indirect charge transfer process as was evidenced by EIS measurements.