Photodegradation Of Pollutants In Water Research Articles

Cornstalk hydrochar produced by phosphoric acid-assisted hydrothermal carbonization for effective adsorption and photodegradation of norfloxacin

Hydrochars have been widely applied in removing pollutants from aqueous solutions. In this study, hydrochars synthesized by H3PO4-assisted hydrothermal carbonization (HC-xPs) were used to remove norfloxacin (NOR) from water through synergistic adsorption and photodegradation. HC-xPs showed the morphology of carbon microspheres with an average diameter of 0.3 μm. The specific surface area of the hydrochar carbonized with 5 mol/L H3PO4 (HC-5P) was 11.2 times higher than that of the pristine hydrochar (HC). Furthermore, phosphorus-containing functional groups were introduced to HC-5P, beneficial to its adsorption of NOR. The highest NOR adsorption was achieved on HC-5P with the maximum Langmuir capacity of 69.1 mg g−1, owing to multiple mechanisms including electrostatic effects, π-π interactions, hydrophobic interactions, and hydrogen bonding. Compared with HC, HC-5P also demonstrated increased visible light absorption capacity. The first-order rate constant of HC-5P on combined adsorption and photodegradation of NOR was 12.0 times of HC. The photodegradation intermediates were identified by HPLC-MS to understand NOR degradation pathways. This work can be extended to the preparation of low-cost and highly efficient hydrochars for adsorption and photodegradation of pollutants in water.

MOF based nanocomposites for photocatalytic degradation of pollutants in water: A critical review

Metal-organic framework (MOF) based nanocomposites have a wide range of applications; however, research output indicates that MOF based nanocomposites have attracted great attention in the area of water treatment, particularly photodegradation of water pollutants. This comes as a result of high water pollution, water scarcity, poor drinking water quality and the emerging of tenacious micropollutants found in water bodies. Majority of water pollutants can be treated via photocatalytic processes and MOF is a remarkable modifying and support material for photocatalytic nanomaterials. MOF have tremendous physicochemical properties which provide opportunities for unique fabrication and modification of photocatalytic nanocomposites with enhanced efficiency, recovery, recyclability and reusability in water treatment. In this review, MOF-based nanocomposites, fabrication techniques, classifications, mechanisms as well as challenges and future prospects for the photocatalytic degradation of pollutants in water are investigated and discussed.

Spectral Engineering of Hybrid Biotemplated Photonic/Photocatalytic Nanoarchitectures.

Solar radiation is a cheap and abundant energy for water remediation, hydrogen generation by water splitting, and CO2 reduction. Supported photocatalysts have to be tuned to the pollutants to be eliminated. Spectral engineering may be a handy tool to increase the efficiency or the selectivity of these. Photonic nanoarchitectures of biological origin with hierarchical organization from nanometers to centimeters are candidates for such applications. We used the blue wing surface of laboratory-reared male Polyommatus icarus butterflies in combination with atomic layer deposition (ALD) of conformal ZnO coating and octahedral Cu2O nanoparticles (NP) to explore the possibilities of engineering the optical and catalytic properties of hybrid photonic nanoarchitectures. The samples were characterized by UV-Vis spectroscopy and optical and scanning electron microscopy. Their photocatalytic performance was benchmarked by comparing the initial decomposition rates of rhodamine B. Cu2O NPs alone or on the butterfly wings, covered by a 5 nm thick layer of ZnO, showed poor performance. Butterfly wings, or ZnO coated butterfly wings with 15 nm ALD layer showed a 3 to 3.5 times enhancement as compared to bare glass. The best performance of almost 4.3 times increase was obtained for the wings conformally coated with 15 nm ZnO, deposited with Cu2O NPs, followed by conformal coating with an additional 5 nm of ZnO by ALD. This enhanced efficiency is associated with slow light effects on the red edge of the reflectance maximum of the photonic nanoarchitectures and with enhanced carrier separation through the n-type ZnO and the p-type Cu2O heterojunction. Properly chosen biologic photonic nanoarchitectures in combination with carefully selected photocatalyst(s) can significantly increase the photodegradation of pollutants in water under visible light illumination.

MoS2 and MoS2 Nanocomposites for Adsorption and Photodegradation of Water Pollutants: A Review.

The need for fresh and conveniently treated water has become a major concern in recent years. Molybdenum disulfide (MoS2) nanomaterials are attracting attention in various fields, such as energy, hydrogen production, and water decontamination. This review provides an overview of the recent developments in MoS2-based nanomaterials for water treatment via adsorption and photodegradation. Primary attention is given to the structure, properties, and major methods for the synthesis and modification of MoS2, aiming for efficient water-contaminant removal. The combination of MoS2 with other components results in nanocomposites that can be separated easily or that present enhanced adsorptive and photocatalytic properties. The performance of these materials in the adsorption of heavy metal ions and organic contaminants, such as dyes and drugs, is reviewed. The review also summarizes current progress in the photocatalytic degradation of various water pollutants, using MoS2-based nanomaterials under UV-VIS light irradiation. MoS2-based materials showed good activity after several reuse cycles and in real water scenarios. Regarding the ecotoxicity of the MoS2, the number of studies is still limited, and more work is needed to effectively evaluate the risks of using this nanomaterial in water treatment.

Impact of Gd3+ doping on structural, electronic, magnetic, and photocatalytic properties of MnFe2O4 nanoferrites and application in dye-polluted wastewater remediation.

The present work focuses on developing Gd-doped Mn spinel nanoferrites and their potential application in the photodegradation of water pollutants. The impact of Gd3+ ion substitution on structural, electronic, and magnetic characteristics of manganese ferrites has been studied. Nanocrystalline samples of MnGdxFe2-xO4 (x = 0.0 to 0.10, in step size of 0.02) ferrites were prepared via sol-gel self-ignition route. The Rietveld, XPS, HRTEM, and SAED characterization methods confirmed the formation of phase pure ferrite nanoparticles (~ 8-22nm) in the cubic spinel structure. The Gd3+ content in these nanoferrites responded to a systematic reduction in the size of nanocrystallites and an upsurge in the density of nanoferrites. The XPS study revealed fine assimilation of constituent elements in the fcc lattice and ruled out impurities in the nanoferrites. The Fe and the Gd ions were found to be in Fe3+ and Gd3+ states, respectively. While a major fraction of the Mn ions were found to be in the Mn2+ state, a small fraction of Mn4+ ions was observed on the surface of nanoparticles. The nanoferrites were found to exhibit a soft ferromagnetic state from 300 to 20K limits. The highest saturation magnetization was observed for x = 0.02 (MS = 66.6emu/g at 20K). The observed magnetic properties can be understood with the competing (Fe3+ and Mn2+)A-O2--[Fe3+, Mn2+, and Gd3+]B superexchange interactions and magnetocrystalline anisotropy. Due to the small band gap energy of Gd-doped Mn ferrites than that of the pure Mn ferrite, they have demonstrated excellent photocatalytic activity for the degradation of methylene blue (MB) dye under visible light illumination. As much as 96.35% of the MB dye was found to get degraded in 70min of light illumination over synthesized nanoparticles and the photodegradation reaction followed pseudo-first-order kinetics. The increased optical absorbance due to lower band gap, suppressed recombination rate of charge carriers, and enhanced charge mobility make them effective visible light active photocatalysts. This study revealed that the electronic, optical, and magnetic properties of MnFe2O4 nanoferrites could be easily tuned by varying the Gd3+ content and the prepared Gd-doped MnFe2O4 nanomaterials have boundless potential to be utilized in the future making promising active photocatalysts and degradation of harmful industrial dyes for enhanced protection in the fields of environment and health care.

Ingenious construction of Ni(DMG)2/TiO2-decorated porous nanofibers for the highly efficient photodegradation of pollutants in water

Dyes and metal ions which are the major components of effluents from industries such as textile, paper, leather, cosmetics and plastic, prove to be the most harmful and toxic of all the contaminants. Especially, Ni2+ as colorant and methylene blue (MB) are contained in the wastewater of printing and dyeing plant. Herein, novel porous dimethylglyoxime (DMG)/TiO2/polyacrylonitrile (PAN) nanofiber mats were prepared via electrospinning to treat Ni2+ and MB mixture pollutants. The formation of red and virgulate Ni(DMG)2 on the nanofiber surface indicated that the composite possessed visible adsorption capacity (48.6895 mg g−1 in 120 min) as a benefit of the capability of DMG to sense Ni2+. Most importantly, the DMG/TiO2-decorated PAN nanofiber mats exhibited excellent photocatalytic MB degradation efficiency (97 % within 60 min) owing to the construction of heterjunctions between Ni(DMG)2 and TiO2 nanoparticles and the shortening of electron and hole transport paths by hierarchical structures. The skillful use of Ni(DMG)2 as an intermediate for photocatalytic MB degradation suggested that these functionalized nanofiber mats are promising candidates for practical application in sensing, heavy metal ion adsorption, and photocatalytic organic pollutant degradation.

Hybrid sonoprecipitation fabrication of magnetic ZnO-GO-Fe3O4 nanophotocatalyst for solar-light-driven degradation of dyes in water

ZnO-GO-Fe3O4 as an effective magnetic nanocomposite in photodegradation of water pollutants is prepared via two step procedure and its photocatalytic activity for organic dyes degradation is investigated. The first step is sonoprecipitation synthesis of ZnO over graphene oxide nanosheet and the second step is addition of Fe3O4 nanoparticles by two methods: precipitation synthesis and solvothermal addition. X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray Analysis (EDX), Transmission Electron Microscopy (TEM), Brunauer-Emmett-Teller (BET) Surface Area Analysis and Barrett-Joyner-Halenda (BJH) Pore Size and Volume Analysis, Differential reflectance spectroscopy (DRS), Fourier Transform Infrared spectroscopy (FTIR) and Vibrating-Sample Magnetometer (VSM) techniques are employed to examine the characterization of the nanocomposites. The results display high surface area with mesoporous structure and low energy band gap is obtained for ZnO-GO-Fe3O4 synthesized via solvothermal method. Also, ultrasound irradiation increases the available surface area for photoreaction. The degradation percent of eosin yellow and methylene blue are about 60 and 97%, respectively. The effect of initial pH of solution, the amount of loaded photocatalyst and initial dye concentration are investigated in this research.

FOTODEGRADACIÓN DEL COLORANTE AZUL ERIONYL EN AGUA MEDIANTE LUZ SOLAR Y CATALIZADORES DE PALADIO

In this investigation, the degradation of blue dye erionyl was evaluated in aqueous medium by photocatalysis with solar radiation. Six catalysts of palladium supported on combinations of aluminum-cerium–zirconium oxides were synthesized by the sol-gel method and impregnation. Materials used as supports were characterized by XRD, meanwhile catalysts were analyzed by SEM and EDS techniques. The Degussa TiO2 commercial was used as reference for evaluating the performance of the palladium catalysts in the photocatalytic processes, since is widely used as an efficient catalyst for photodegradation of pollutants in water. The photocatalytic processes were carryout in a system with borosilicate reactors and high reflectance aluminum foil compound parabolic collectors. The six palladium catalysts achieved a percentage degradation of erionyl blue dye higher than 60%, having the best performance the palladium supported on alumina with 97% degradation after 5 hours of photocatalytic process. It is noteworthy that this catalyst showed a better performance than the TiO2 catalyst reached up to 81% degradation.

Solvent effects on microstructures and properties of three-dimensional hierarchical TiO2 microsphere structures synthesized via solvothermal approach

One-step solvothermal method has been proved to be a simple and efficient route to synthesize three-dimensional (3D) hierarchical TiO2 microsphere structures, but discrepant properties of the solvent media had been claimed as the major factors determining microstructures and properties of the final products. In this study, several typical solvents, including alkane, aromatic hydrocarbons, halohydrocarbon, ketone, organic acid, mono- and dihydric alcohols, were selected to comprehensively investigate the effect of solvents on the morphology, crystal structure, specific surface area, porous property and light harvesting capability of the final products. According to the experimental results, a good interface separating titanium precursor with aqueous phase in the reaction solution, created by non-polar solvents, or polar solvents which are immiscible with titanium precursor, was the decisive factor for the formation of quasi-3D urchin-like TiO2 microspheres self-assembled from one-dimensional (1D) nanostructures, and concentrated H+ induced by organic acid medium was also helpful. Meanwhile, without the liquid-liquid interface or extremely low solution pH, anatase TiO2 sphere structures with big specific surface area comprising of nanoparticles or nanosheets would be formed, and performed well in photodegradation of pollutants in water.

Mixed-phase TiO2 photocatalysis: correlation between phase composition and photodecomposition of water pollutants

Abstract In most cases, the combination of both anatase (up to 80%) and rutile (up to 20%) structures in a mixed-phase TiO2 semiconductor results in a better photocatalytic performance compared to the pure phase. The improvement from anatase to rutile is brought about by the enhanced transportation of photogenerated electrons. This consequently results in improved efficiency of the photoelectric and photocurrent conversion. This review highlights the effects of the morphology, particle size, and crystal structure of mixed-phase TiO2 toward the photodegradation of water pollutants. It was demonstrated that the synergistic effect between anatase and rutile TiO2 due to the interfacial electron transfer from rutile to anatase improved the photocurrent as well as the overall conversion efficiency of the anatase photoanodes. The morphologies of mixed-phase TiO2 also contributed to the final photodegradation properties. The charge and electron transfer of mixed-phase TiO2 improved the 1D structure. This consequently enables photodegradation at the visible light range.

A novel Zn–TiO2/C@SiO2 nanoporous material on rice husk for photocatalytic applications under visible light

A series of self-nitrogen-doped and Zn-doped TiO2/C@SiO2 (ZTRH) nanoporous composites with high surface area and excellent biological hierarchical porous structure have been synthesized by sol–gel method at different temperatures. The porous SiO2 and activated carbon from the decomposition of rice husk (RH) were regarded as the template and porous catalytic carrier. The structure, crystallinity, morphology, and other physical–chemical properties of the samples were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transforminfrared spectroscopy, N2 adsorption–desorption isotherms, and UV–vis diffuse reflectance spectroscopy. The feasibility of ZTRH nanoporous composites for decomposing pollutants was evaluated by rhodamine B under visible light irradiation. Compared with the traditional photocatalytic materials, ZTRH nanoporous materials not only performed high efficiency in pollutants degradation, but also exhibited good adsorption properties. Moreover, since RH ash acts as the catalyst support, the composites are easily recycled after catalysis reaction. The ZTRH nanoporous composites could be applied to the wastewater with different pH values and be regarded as a kind of promising recyclable photocatalyst in photodegradation of pollutants in water.

Enhancement of Photocatalytic Efficiency of TiO2 by Supporting on Clinoptilolite in the Decolorization of Azo Dye Direct Yellow 12 Aqueous Solutions

AbstractStructure and physico‐chemical properties of a photocatalyst, especially surface area and absorption ability, were correlated to catalytic activities in photodegradation of dye pollutants in water. In this investigation photocatalytic degradation of azo dye Direct yellow 12 (Chrysophenine G) in water was studied. Titanium(IV) oxide was supported on Clinoptilolite (CP) (Iranian Natural Zeolite) using solid‐state dispersion (SSD) method. The results show that the TiO2/Clinoptilolite (SSD) is an active photocatalyst. The maximum effect of photo degradation was observed at 10 wt.% TiO2, 90 wt.% Clinoptilolite. A first order reaction with k = 0.0108 min−1 was observed. The effects of some parameters such as pH, amount of photocatalyst, initial concentration of dye were examined.

Development of Visible Light Sensitive TiO<sub>2</sub> Photocatalysts and Their Sensitization Using Fe<sup>3+</sup> Ions

Titanium dioxide photocatalysts are promising substrates for photodegradation of pollutants in water and air, but show photocatalytic activities only under UV light. To utilize a wider range of incident wavelengths such as solar light, development of photocatalysts active under visible light is very important. Chemically modified titanium dioxide photocatalysts were prepared containing anatase phase with S (S4+) substituted for some lattice Ti atoms or N substituted for some lattice O atoms. These catalysts showed strong absorption of visible light and high activities for degradation of 2-propanol in aqueous solution and partial oxidation of adamantane under irradiation at wavelengths longer than 440 nm. The oxidation states of the S and N atoms incorporated into the TiO2 particles were determined to be mainly S4+ and N3− from XPS spectra, respectively. The photocatalytic activities of S- or N-doped TiO2 photocatalysts with adsorbed Fe3+ ions were markedly improved for oxidation of 2-propanol compared to those of S- or N-doped TiO2 without Fe3+ ions under a wide range of incident wavelengths, including UV light and visible light. The photocatalytic activity reached maximum with 0.90 wt% Fe3+ ions adsorbed on S-doped TiO2, and 0.36 wt% Fe3+ ions on N-doped TiO2. Furthermore, redox treatment of S- or N-doped TiO2 photocatalysts with adsorbed Fe3+ ions by reduction with NaBH4 followed by air oxidation resulted in further improvements in photocatalytic activities. In this case, the optimum amounts of Fe3+ were 2.81 and 0.88 wt% on the surfaces of S- and N-doped TiO2 photocatalysts, respectively.

Preparation of photocatalytic TiO 2 coatings of nanosized particles on activated carbon by AP-MOCVD

Anatase TiO 2 coatings on highly porous activated carbon were prepared by a novel method—atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD). At a source temperature of 423 K, the TiO 2 particles were mostly coated on the external surface of activated carbon. These particles were well dispersed with their sizes ranging from 10 to 50 nm. The optimum loading of TiO 2 was found to be 12 wt%. The TiO 2 photocatalysts so prepared behave similarly to that of the pure commercial TiO 2 powder. The activated carbon supported TiO 2 catalyst could be easily separated from the treated water with its catalytic performance maintained even after 10 cycles, indicating that the TiO 2 coating was stable. It was observed that TiO 2 supported on activated carbon had a high capacity to mineralize pollutants. Consequently, activated carbon supported TiO 2 by AP-MOCVD is a promising photocatalyst for the photodegradation of pollutants in water.

Preparation of S-doped TiO 2 photocatalysts and their photocatalytic activities under visible light

Although titanium dioxide photocatalysts having anatase phase are a promising substrate for photodegradation of pollutants in water and air, their photocatalytic activities show only under ultraviolet (UV) light. For us to utilized a wide range of incident light such as solar light, development of the photocatalysts whose activities show under visible light is one of the most important strategies. We have synthesized chemically modified titanium dioxide photocatalysts in which S (S 4+) substitutes for some of the lattice titanium atoms. They show strong absorption for visible light and high activities for degradation of methylene blue, 2-propanol in aqueous solution and partial oxidation of adamantane under irradiation at wavelengths longer than 440 nm. The oxidation state of the S atoms incorporated into the TiO 2 particles is determined to be mainly S 4+ from X-ray photoelectron spectra (XPS) spectra.

Preparation of visible light active S-doped TiO2 photocatalysts and their photocatalytic activities

Although titanium dioxide photocatalysts having an anatase phase are a promising substrate for photodegradation of pollutants in water and air, their photocatalytic activities show only under UV light. To utilize solar light which has a large amount of visible light, the development of the photocatalysts whose activities show under visible light is one of the most important strategies. We have succeeded in synthesizing chemically modified titanium dioxide photocatalysts in which S (S4+) substitutes for some of the lattice titanium atoms. They show strong absorption for visible light and high activities for degradation of 2-propanol in aqueous solution and partial oxidation of adamantane in acetonitrile under irradiation at wavelengths longer than 440 nm. The oxidation state of the S atoms incorporated into the TiO2 particles is determined to be mainly S4+ from XPS spectra.