Photocatalytic Degradation Of Aqueous Solution Research Articles

Role of ZnO/GO nanocomposite in photocatalytic degradation of mixture of organic pollutants and antimicrobial activity

AbstractA number of carcinogenic dyes and microbial infections have negative effects on living being. These also have a detrimental effect on water quality and responsible for major health problems. ZnO/GO nanocomposites (NCs) (10 wt. % GO) is synthesized via one pot ecofriendly route. It is utilized for photocatalytic degradation of aqueous solution of Malachite green (MG), Crystal violet (CV) and first time mixture of pollutants (CV+MG) dyes in 1 : 2 ratio. These synthesized NCs are analyzed by using many techniques such as P‐XRD, FE‐SEM, HR‐TEM, BET and UV‐Vis spectrophotometer. Kinetics and mechanism of photocatalytic degradation is also explored. The photocatalytic degradation followed the order (CV+MG) (1 : 2) binary system > MG > CV dyes. On the other hand, an antibacterial activity is also investigated against Gram positive (+ve) bacteria such as Staphylococcus aureus (S. aureus), Enterococcus faecalis (E. faecalis) as well as Gram negative (−ve) bacteria such as Escherichia coli (E. coli), and Citrobacter sp. The ZnO/GO NCs followed the antibacterial activity order: E. coli > S. aureus ~ Citrobacter sp. > E. faecalis and the inhibition zones diameters are 20, 15, 15 and 10 mm respectively which is comparable with standard drug Gentamycin.

Superior photocatalytic performance of ancillary-oxidant-free novel starch supported nano MFe2O4 (M = Zn, Ni, and Fe) ferrites for degradation of organic dye pollutants

This work presents the effectual degradation of MB and MO dyes in an aqueous solution under UV light irradiation on nano ZnFe2O4, NiFe2O4, and Fe3O4 without using any supplementary oxidants has been reported. Nano ZnFe2O4, NiFe2O4, and Fe3O4 are successfully prepared via a co-precipitation technique utilizing biodegradable starch as a surfactant. XRD patterns reveal a pure spinel phase for all the samples. FTIR spectra confirm the successful embedding of the starch surfactant. SEM micrographs exhibit tiny spherical particles of size 5–8 and 4–6 nm for ZnFe2O4 and NiFe2O4 but spherical particles of 8–10 nm and flake-like particles of ∼14 nm thick for Fe3O4. N2 sorption studies show type-IV isotherms typical of mesoporous structures. The direct bandgap of these ferrite nanoparticles is 2.03–2.15 eV, related to the metal D-d onsite transfers, which are permitted by spin but prohibited by parity. MB decolorization of 99% is achieved in less than 2 h for all the samples; in contrast, MO decolorization takes relatively longer irradiation. The decolorization kinetics suggests that the pseudo-second-order model is more appropriate to explain the decolorization process of MB and MO by the catalysts. The order of photocatalytic activity evaluated from rate constant (k1) per SSA values is Fe3O4 < ZnFe2O4 < NiFe2O4 for both MB and MO decolorization. NiFe2O4 photocatalyst shows the best effect on the decolorization of both dyes due to its low bandgap and high surface area. All the ferrite catalysts demonstrate high stability with no substantial deterioration of photocatalytic activity even after three cycles. The results of this study endorse that the nano ferrites prepared in this work are potential candidates for the photocatalytic degradation of aqueous solutions of MB and MO.

Silane modification of TiO2 nanoparticles and usage in acrylic film for effective photocatalytic degradation of methylene blue under visible light

To fabricate a photocatalytic acrylic paint, TiO2 nanoparticles were surface modified by a bi-functional amino silane (i.e. bis-3-(aminopropyltriethoxysilane)) at different concentrations and applied at 1, 3 and 5 wt% to an acrylic latex. It was found that the surface modification of nano TiO2 enhanced its specific surface area about 42%. The tensile properties of the pristine and nanocomposite acrylic films were assessed. The photocatalytic degradation of aqueous solution and stain of methylene blue (MB) were evaluated (under solar, visible, and UV illuminations) by nanoparticles and nanocomposites, respectively. Results showed that incorporating 3 wt% of the pure and modified nano TiO2 to arylic film caused 62 and 144% increment in the tensile strength. The modified nanoparticles showed higher MB degradation contents under UV, visible and solar irradiation (82, 70, 48%, respectively). The addition of pure and modified nanoparticles to the acrylic film caused decrement in the water contact angle from 84 to 70 and 46°, respectively. It also caused considerable enhancement in the glass transition temperature (Tg) of acrylic film compared to the pristine and pure nanocomposite films (i.e. about 17 and 9 °C, respectively). Furthermore, it was found that the modified nanocomposite caused more color change of MB stain (65%).

Structure and optical, magnetic and photocatalytic properties of Cr3+ substituted zinc nano-ferrites

In this paper, the Cr3+ substituted zinc ferrite (ZnCrxFe2-xO4 with x = 0, 0.15 and 0.25) nanoparticles with single cubic spinel structure (Fd-3 m space group) were prepared by chemical co-precipitation method, and their structure and optical, magnetic and photocatalytic performaces were investigated. With Cr added, the lattice parameter and average grain size of the ferrites remarkably changed. High-quality nanostructured ferrite with an average particle size of 22–31 nm are revealed by TEM and SEM. The vibrational stretching modes of tetrahedral and octahedral sites were confirmed by FTIR. The optical studies proved a gradual decrease in the optical band gap which indicated the emergence of sub-band-gap energy levels by the chromium content. The magnetic properties were investigated through magnetization technique. The saturation magnetization measured from M-H hysteresis plot show decreasing trend with increase in Cr3+ content. The photocatalytic degradation of aqueous solution of Methyl Orange (MO) in the presence of prepared nano-ferrite under visible-light irradiation has been studied and discussed. The photodegradation efficiency of MO over ZnCrxFe2-xO4 photocatalysts is enhanced; (69%, 74% and 82% with increasing Cr3+content, respectively) compared with its modest value 12% without addition.

Removal of micro-pollutant using an indigenous photo membrane reactor

Pharmaceutical wastewater treatment using heterogeneous photocatalysis in presence of TiO2 nanoparticles has become a lucrative method because the convectional wastewater and biological treatments usually fail to remove the detrimental effect of different drugs and hormones on the environment. The nanoparticles recovery and reuse is the most challenging task in practice. The main goal of the present study is to recover and reuse of photocatalyst by immobilizing it on the membrane surface. Consequently, two types of immobilization technique have been used here, one is surface immobilization by dipped coating, and other is impregnation of catalyst during fabrication of the membrane. To conduct photocatalysis, an indigenous photo membrane reactor has also been fabricated during the research work. The presence of TiO2 nanoparticles has not only improved the catalytic property of the membrane, but also the contact angle analysis has confirmed the enhanced hydrophilic as well as antifouling property of the surface modified membrane. The fabricated membranes were characterized by scanning electron microscopy (SEM). To analyses the performance of photo membrane reactor as well as TiO2 coated or impregnated membranes, the photocatalytic degradation of aqueous solution of chlorhexidine digluconate (CHD), an antibacterial drug, was performed using the developed system and the removal percentage of CHD obtained from the system was found to be quite appreciable. The results show that the recovery and reuse of the catalyst by the present system is very much significant. Meanwhile, the developed reactor can be operated in cross flow configuration under batch, semi-batch and continuous mode.

Sputtered vs. sol-gel TiO2-doped films: Characterization and assessment of aqueous bisphenol A oxidation under UV and visible light radiation

In this work, TiO2 thin films were deposited onto soda lime glass substrate by two different techniques: sol-gel (SG) and sputtering (SP). The photocatalytic film performance was assessed in a batch recycle reactor testing the photocatalytic degradation of aqueous solutions of bisphenol A (BPA). The use of supported catalysts in batch recycle reactor systems for the photocatalytic degradation of organic pollutants in waste water can be an alternative to nowadays more used slurry batch reactor systems and powdered catalysts, since it is more economically sustainable and not requiring the removal of catalyst particles after waste water treatment. The best photocatalytic activities were achieved with SG films due to their porosity, which allows BPA molecule to better access the catalytic site than in case of SP films. Raman spectroscopy also showed that SP films have more oxygen vacancies, which may end up acting as charge recombination centers. Doping of TiO2 thin films, either with N or Cu, enabled us to trigger the catalytic activity of films also under UV-free visible light radiation. Regardless the order of stacking in the double-layered films, the latter did not result in an increased catalytic activity towards the photodegradation of BPA.

Effect of operational parameters on the photocatalytic degradation of Methylene blue dye solution using manganese doped ZnO nanoparticles

Abstract Photocatalytic degradation of aqueous solution of methylene blue dye under UV light illumination was studied by using manganese doped ZnO ( Z n 1 - x M n x O , where x = 0.00 , x = 0.02 a n d x = 0.05 ) nanoparticles as a photocatalyst. The nanophotocatalysts were synthesized by wet chemical co-precipitation method. The structural, morphological, and optical properties of the photocatalysts were done by X-ray diffraction (XRD), Scanning Electron microscope (SEM), Energy Dispersive X-Ray (EDX), photoluminescence (PL), Fourier Transform Infrared Ray (FTIR) and UV–visible spectroscopic techniques. An improved photocatalytic efficiency of ZnO was observed upon doping with Mn and 2% Mn-doped ZnO exhibited the highest photocatalytic activity among the doped samples. The effect of operating parameters such as amount of catalyst, the initial dye concentration, and initial pH on the rate of dye degradation using 2% Mn-doped ZnO was studied. Under the optimum operation conditions, approximately 99% of dye removal was achieved after 120 min of irradiation.

Visible-light photocatalytic degradation of ethidium bromide using carbon- and iron-modified TiO2 photocatalyst

Nanosized TiO2 as well as carbon (C) and C, Fe co-doped TiO2 were synthesized using reverse microemulsion method. Thermal stability of precursor was studied using thermogravimetry and differential thermal analysis techniques. Heat-treated powders were characterized using Fourier transform infrared spectrophotometer, X-ray diffractometer, scanning electron microscope, transmission electron microscope and energy-dispersive X-ray spectroscope. Visible-light photocatalytic degradation of aqueous solution of ethidium bromide (EtBr) was investigated using C, Fe co-doped TiO2 photocatalyst. UV–visible spectrophotometer and high-pressure liquid chromatography techniques were used to analyze the concentration of EtBr during the degradation process. Various parameters affecting the photocatalytic activity of photocatalyst are studied. C-doped TiO2 acts as photosensitizer and helps to extend the light absorption wavelength of C-doped TiO2.·Fe co-doping introduces new energy levels of the transition metal ions between the band gap of TiO2 and further extends absorption wavelength in visible region. The synergistic effects of C- and Fe-modified TiO2 nanoparticles were responsible for improving visible-light photocatalytic activity.

TiO2 quantum dots for the photocatalytic degradation of indigo carmine dye

In this work, we report the synthesis of TiO2 quantum dots using a simple sol–gel, template free method. The synthesized quantum dots were further studied for their crystalline, morphological, chemical and photo-luminescent properties by using various techniques. The detailed studies revealed that the synthesized TiO2 quantum dots possess well-crystalline pure anatase phase and exhibited good photo-luminescent properties. Further, the catalytic behavior of synthesized quantum dots was monitored by photo-catalytic degradation of aqueous solution of Indigo carmine dye under UV-light irradiation. The reaction conditions were varied so as to optimize catalyst dose, initial dye concentration, pH and reaction temperature. It was found that reaction was facilitated with optimum catalyst dose of 0.75 g/L, low dye concentrations, acidic pH and ambient reaction temperature condition of 25 °C. The reaction kinetic was studied and it was found that the indigo carmine dye photo catalytic degradation followed pseudo first order reaction kinetics with rate constant, k of 0.023 min−1.

Thermal/plasma treatment effect on photocatalytic degradation of aqueous solution of methylene blue using Au-doped Fe/TiO2 photocatalyst

The effect of thermal/plasma treatment on the photocatalytic degradation of methylene blue (MB) using Au-doped Fe/TiO2 photocatalyst was investigated. Iron (Fe)-doped TiO2 samples were prepared by solgel auto-combustion technique. Later, gold nano-particles (AuNPs) were deposited on the as-prepared support (Fe/TiO2) using conventional deposition–precipitation method with NaOH (DP NaOH), and the resulting catalysts were subsequently modified with thermal (at 450°C under vacuum) and plasma (at an ambient temperature under Argon atmosphere for 20 min) treatments. To evaluate particle structure, size distribution, and composition, diverse analytical techniques such as X-ray diffractometer, BET surface area, SEM, EDX, and TEM were used. The photocatalytic activity was evaluated by assessing the degradation of the MB in water under ultraviolet (UV) irradiations while the parameters affecting photocatalytic process such as the catalyst crystallinity, light absorption efficiency, the dosage of catalyst, dopant, and MB concentrations were well controlled. Thermal-/plasma-treated samples showed significant enhancement in the photocatalytic activity compared to untreated samples by changing the morphology, increasing the number of AuNPs, improving the Au-doped Fe/TiO2 interface, and decreasing the band-gap energies thus tuned Au-doped Fe/TiO2 catalyst to higher efficiency. The AuNPs deposited on the Fe/TiO2 showed good thermal stability as well. Based on the obtained results, it can be expected that the modified catalyst may have potential applications in various advanced technologies such as water treatment, sustainable energy, clean environment, and several others.

UV-absorption--the primary process in photocatalysis and some practical consequences.

TiO2 photochemistry studies generally address reactions of photogenerated charge-carriers at the oxide surface or the recombination reactions which control the proportion of charge carriers that reach the surface. By contrast, this review focuses on UV absorption, the first photochemical step in semiconductor photocatalysis. The influence of particle size on absorption and scattering of light by small TiO2 particles is summarized and the importance of considering, the particle size in the application, not the BET or X-ray line broadening size, is emphasized. Three different consequences of UV absorption are then considered. First, two commercially important systems, pigmented polymer films and paints, are used to show that TiO2 can protect from direct photochemical degradation. Then the effect of UV absorption on the measured photocatalytic degradation of aqueous solutions of organics is considered for two separate cases. Firstly, the consequences of UV absorption by TiO2 on the generation of hydroxyl radicals from H2O2 are considered in the context of the claimed synergy between H2O2 and TiO2. Secondly, the effect of altered UV absorption, caused by changed effective particle size of the catalyst, is demonstrated for photocatalysis of propan-2-ol oxidation and salicylic acid degradation.

Optimization of photocatalytic process parameters for the degradation of acrylonitrile using Box Behnken Design

The present study involves the photocatalytic degradation of aqueous solution of acrylonitrile (ACN) which was carried out in a batch reactor under UV light. The degradation efficiency was evaluated with ZnO as a photocatalyst and hydrogen peroxide as an oxidant for a period of 5 h. The variables examined in this study included ZnO dose (0.5–3.0 g/L), pH (2–12), and H2O2 concentration (2.5–10 m mol/L). The rate of degradation was studied in terms of changes in concentration of the pollutant using spectrophotometry. The optimal values of operational parameters leading to degradation of ACN were obtained using Box Behnken design (BBD) under response surface methodology (RSM). The optimum conditions were found to be ZnO dose of 1.48 g/L; pH 7.0 and hydrogen peroxide (H2O2) concentration of 4.22 m mol/L. Under optimum condition, the degradation efficiency of ACN was found to be 89.6%. Optimization of photocatalytic process parameters for the degradation of ACN by BBD under RSM effectively copes with interaction between optimizing variables and its prediction agreed well with the experimental result.

Effect of calcium oxalate on the photocatalytic degradation of Orange II on ZnO surface

The photocatalytic degradation of aqueous solution of Orange II, has been investigated in the presence of ZnO catalyst with calcium oxalate as sacrificial agent. This study demonstrated that the performance of ZnO photocatalyst can be improved by addition of calcium oxalate. Results show that adsorption is an important parameter controlling the degradation phenomena. Indeed, the added oxalate causes a drop in the pH medium, what causes a better adsorption of Orange II on the ZnO surface. The effect of calcium oxalate is to increase the concentration of superoxides (O 2 ·− ) and hydroperoxides (HO2·) radicals, which are key intermediaries in the mechanism of photodegradation because of their powerful force of oxidation.

Photocatalytic Degradation of Solophenyl Red 3 BL in an Aqueous Suspension of Titanium Dioxide

The wastewater from the textile industry generates a serious problem for environment by the presence of compounds such as dyes, resistant to the natural and conventional treatment. In this work, the photocatalytic degradation of aqueous solution of an azo-dye as Solophenyl red 3 BL was investigated, using a semiconductor (TiO2) and a UV lamp. The decolorization of dye aqueous solution was controlled by spectrophotometry. Photolysis is enhanced by the addition of TiO2 particles. The degradation rate depends on the initial pH of the suspension and it goes through a minimum at neutral pH. For a fixed concentration of dye, degradation rate increases with the oxygen concentration and temperature. The influence of temperature on the rate constant corresponds to activation energy of 31.9 kJ/mol. Intensity and geometry of UV radiation and the addition of hydrogen peroxide, are significant parameters whose influence is directly related to changes in the concentrations of OH• and O?• 2 radicals.

Li‐doped nanosized TiO2 powder with enhanced photocalatylic acivity under sunlight irradiation

AbstractThis work reports on the synthesis of Li‐doped TiO2 nanoparticles using the sol–gel process and solid‐state sintering, and investigates their potential use as a photocatalyst for degradation under sunlight excitation of different organic model compounds in aqueous solution. The structure of the nanocrystals was examined by X‐ray diffraction, UV‐vis ground state diffuse reflectance absorption spectra and X‐ray photoelectron emission spectroscopy. Results showed that samples prepared by sol–gel process and calcined at 400 °C are composed of a mixture of anatase and rutile phases, in contrast to the one prepared by solid‐state sintering, which exhibits an anatase phase with Li being involved in a spinel phase. The photocatalytic degradation of aqueous solutions of different aromatic compounds was successfully achieved under sunlight excitation in presence of Li‐doped TiO2 prepared via sol–gel process. It was shown that the calcination temperature and the preparation mode greatly affect the photocatalytic efficiency. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Photocatalytic Degradation of Bismarck Brown G Using Irradiated ZnO in Aqueous Solutions

In this study, a homemade photoreactor equipped with 125w/542 high pressure mercury lamp as a source for near‐UV radiation, was used for photocatalytic degradation of aqueous solutions of Bismarck brown G, (C18H20N8Cl2),4‐[5‐(2,4‐Diamino‐5‐methylphenyl)diazenyl‐2‐methylphenyl] diazenyl ‐6‐methylbenzol‐1,3‐diamin using zinc oxide. The disappearance of the original colored reactant concentrations with irradiation time was monitored spectrophotometrically by comparison with unexposed controls. It is noticed that the photocatalytic degradation process was high at the beginning and then decreased with time following pseudo first‐order kinetics according to the Langmuir–Hinshelwood model. The effects of zinc oxide mass, dye concentration and temperature on photocatalytic decolorization efficiency (P.D.E.) were studied. P.D.E. reached 95.76% for Bismarck brown G after 50 minutes of irradiation at 293.15 K P.D.E. was found to increase with increasing temperature and the activation energy of photocatalytic degradation was calculated and found to be equal to 32±1 kJ mol-1.

OPTIMIZATION AND EFFECTS OF SOME ELECTRON ACCEPTORS ON THE PHOTOCATALYTIC DEGRADATION OF DIRECT RED 23 AZO DYE

ABSTRACT The photocatalytic degradation of aqueous solution of commercial azo textile dye, direct red 23 (DR23), was carried out in TiO 2 suspension at 30oC with the use of artificial and solar light sources. The photoreaction followed the first-order behavior with respect to the azo dye as a function of irradiation time. A 2 3 factorial design was carried out, in order to obtain the best experimental conditions, using the rate constant of DR23 degradation as the analytical response. Seven chemical species were determined from the normalized UV-Vis spectra during the DR23 degradation through Imbrie Q mode factor analysis followed by varimax and Imbrie oblique rotations. The addition of electron acceptors, such as H 2 O 2 , S 2 O 82- , and ClO 3- on the optimized conditions, was carried out to increase the DR23 degradation rate. Comparison of degradation efficiencies under artificial and solar radiation was examined in the presence of oxidants. Keywords : degradation; direct red 23; inorganic oxidant; photocatalysis; factorial design.

Degradation of aqueous solutions of camphor by heterogeneous photocatalysis

In this study the photocatalytic degradation of aqueous solutions of camphor was investigated by using TiO 2 and ZnO photocatalysts. In the presence of artificial UV-light the highly photosensitive camphor was almost totally degraded after reaction times of 60 min. However, under these conditions the mineralization degree was lower than 25%. In the presence of semiconductors the degradation was complete after a treatment time of about 30 min. Moreover, the mineralization was considerably greater, mainly with the use of TiO 2 (>80% at reaction time of 60 min). Heterogeneous photocatalytic processes applied in the presence of solar radiation show a promising degradation capability. TiO 2-based processes afforded mineralization degrees of about 90% after a reaction time of 120 min, when the system was assisted by aeration.

Photocatalytic degradation of Remazol Red F3B using ZnO catalyst

The photocatalytic degradation of aqueous solution of a commercial azo-reactive textile dye, Remazol Red F3B, has been investigated in a batch slurry reactor, in the presence of ZnO catalyst using two different UV light sources emitting at 254 nm and 365 nm. The effects of various process variables on degradation performance of the process have been investigated. The results showed that decolourization and total organic carbon (TOC) removal are both affected in the same manner by the solution pH in the pH range 6–10, showing maxima at pH 7 and pH 10. They are inversely related to the dye concentration, they increase in power-law with the light intensity. Decolourization is faster with 365 nm UV. TOC removal is not affected by UV wavelength in the initial period up to 20 min, after which it progresses faster under 365 nm UV radiation. These results indicate that the UV wavelength influences especially the degradation rate of the intermediate products generated during the initial period of the photocatalytic process. Finally, catalyst loading affects both efficiencies in the same trend, which are maximized at about 2 g/l catalyst loading.

Photocatalytic mineralisation of aniline derivatives in aquatic systems using semiconductor oxides.

Photocatalytic degradation of aqueous solution of aniline derivatives such as ortho-nitroaniline (ONA), meta-nitroaniline (MNA), para-nitroaniline (PNA), 4-bromoaniline (4-BrA) and 2-chloroaniline (2-ClA) were carried out over ZnO or TiO2 (anatase and rutile) in a photocatalytic reactor. The observed results revealed that the order of photocatalytic activity for degradation of selected compound was ZnO > TiO2 (rutile) > TiO2 (anatase) with the ratio of the rate constants to the surface area of 3.2 x 10(-3), 1.9 x 10(-3) and 1.0 x 10(-3) respectively. The effect of some physical and chemical parameters such as amount of photocatalyst, pH, time of irradiation and solvent were studied. Degradation kinetic was according to Longmuir behaviour. Spectrophotometric methods and TOC analysis supported that aniline derivatives almost completely mineralized.