Sterilization system for air purifier by combining ultraviolet light emitting diodes with TiO2

BACKGROUND: Ultraviolet light emitting diodes (UV LEDs) were used as a light source in TiO₂ photocatalysis because of their many advantages, such as, long life, safety, low pollution, etc. In this experiment, a light source panel was successfully fabricated with UV LEDs, the light intensities of which were relatively uniform. RESULTS: The sterilization process comprised two steps. First, an aerosol was blocked by high efficient particulate air (HEPA) filter paper coated with TiO₂ photocatalyst. Second, Staphylococcus aureus in the aerosol decreased gradually in the photocatalysis process of UV LED/TiO₂. After 52 h irradiation all the S. aureus were killed. CONCLUSION: The UV LED light source panel had a larger surface for irradiation than a mercury lamp. Thus, its sterilization efficiency was much better than that of traditional methods. The feasibility of UV LED/TiO₂ for photocatalysis was proved. Copyright © 2009 Society of Chemical Industry     

PVDF/ZnO composite films for photocatalysis: A comparative study of solution mixing and melt blending methods

Heterogeneous photocatalysis represents a solution for several environmental problems. However, achieving photocatalyst separation from reaction media on a large scale remains a challenge, one that might be overcome by the immobilization of photocatalysts into supports. To this end, composites of polyvinylidene fluoride and zinc oxide (ZnO) were prepared by three different techniques: solution mixing (SM) followed by Nonsolvent Induced Phase Separation; and melt blending at both low- and high-shear rates (LS and HS) in a rheometer and mixing chamber, respectively, to compare the resultant morphology in photocatalysis. Photocatalytic efficiency was assessed by methylene blue (MB) discoloration in a batch reactor liquid phase and by resazurin (RZ) reduction. The changes promoted by nanoparticle inclusion, processing conditions and UV effect were demonstrated by FTIR-ATR, XRD, DSC, and SEM. Results showed that ZnO incorporation was successful under all processing conditions, providing effective photocatalytic composites. However, samples prepared by SM had a twofold increase in discoloration efficiency and fourfold increase in surface photoactivity, when compared with LS or HS-produced samples, explained by its higher porosity of 88% ± 1.3%. The covering of the photocatalyst surface was also evident on SEM analysis for melt blended samples, further contributing to reduction in their photocatalytic activity.     

Photodegradation of cellulose under UV light catalysed by TiO2

BACKGROUND: Since natural cellulose is an insoluble, crystalline microfibril, which is difficult to react with other compounds, most reactions related with cellulose are heterogeneous. The methods of cellulose degradation include acid hydrolysis, thermal degradation, alkaline degradation and catalytic degradation. Photocatalysis is a very powerful process. RESULTS: With 10 g cellulose dissolved in 100 mL ZnCl₂ solution (66%), the 5‐hydroxymethyl furfural yield in the corrugated plate photocatalytic reactor reached 3.87 g L^?1 under the following experimental conditions: 2 h irradiation under ultraviolet (UV) lamp (power—21 W), nine TiO₂ coating cycles, and 42° corrugated plate angle. CONCLUSION: Owing to the enhancement of catalyst surface area illuminated by UV light and the large number of photons captured on the catalyst surface, the energy efficiency per mass (EE/M) of the corrugated plate photocatalytic reactor for photocatalytic degradation of cellulose was 10.9 kWh kg^?1. This is therefore an effective technology for 5‐HMF preparation from cellulose. Copyright © 2011 Society of Chemical Industry     

Photocatalytic and electrochemically assisted photocatalytic oxidation of formic acid on TiO2 films under UVA and UVB irradiation

Titanium dioxide (TiO₂) photocatalysis is a possible alternative/complementary technology for water purification. Attempts to increase the overall efficiency of the process include using higher energy UV to gain better quantum efficiency and electrochemically assisting the process by the application of an external electrical potential. In this work, nanocrystalline TiO₂ films, prepared on borosilicate glass and indium-doped tin oxide (ITO) borosilicate glass, were used to investigate the photocatalytic and electrochemically assisted photocatalytic oxidation of formic acid under UVA and UVB irradiation. The experiments were carried out in a stirred tank reactor with high mass transfer characteristics. The rate of formic acid oxidation under UVB irradiation was 30% greater as compared to UVA irradiation. A maximum Φ_app of 9% was obtained under UVA irradiation in 100% O₂ under open circuit or +1.0 V (SCE) applied potential. A maximum Φ_app of 20.3% was obtained under UVB irradiation with 100% O₂ using TiO₂ on borosilicate glass. Φ_app was 19% for +1.0 V, 100% O₂, using TiO₂ on ITO borosilicate glass under UVB irradiation. The increase in oxidation rates and Φ_app with UVB irradiation are due to the higher extinction coefficient of TiO₂ at shorter wavelengths and/or the promotion of conduction band electrons to higher more stable states, thus reducing the rate of recombination of charge carriers. The use of a UVB source as compared to a UVA source results in a significant increase in the rate of oxidation and increased apparent quantum yields, however, a cost analysis of the process would be required to determine the economic viability of employing UVB sources. Electrochemically assisted photocatalysis may prove beneficial in large-scale reactors where mass transfer limitations exist.     

Photocatalytic removal of NOx over immobilized BiFeO<Subscript>3</Subscript> nanoparticles and effect of operational parameters

Perovskite type BiFeO₃ (BFO) was synthesized by sol-gel auto-combustion method. Synthesized BFO was immobilized on the micro slides glass plates by sol-gel dip-coating method. The sample was characterized by XRD, FESEM, UV-Vis DRS, and BET techniques. The XRD pattern confirmed the perovskite structure, and from the Debye-Scherrer equation the average crystalline size was calculated as 19 nm. The FE-SEM images of prepared BFO showed porous structure with low agglomeration. The band gap energy was calculated about 2.13 eV, and the specific surface area (SSA) of prepared BFO nanostructure was obtained 55.1m² g^?1. The photocatalytic activity of prepared pure and immobilized BFO was investigated in the removal of NOx under UV irradiation, in the batch photoreactor. The effects of operational parameters such as initial concentration of NOx, light intensity and amount of coated photocatalyst, under identical conditions, were investigated. The results showed that the highest conversion of NOx was obtained as 35.83% in the 5 ppm of NOx with 1.2 g immobilized BFO and under 15 W illumination lamp.     

Comparative study on the sonophotocatalytic degradation of hazardous waste

The enhanced sonophotocatalytic degradation of Chrome Intra Orange G (C.I. 18745), an azo dye, in aqueous solution under UV light has been carried out using solvothermally sensitized ZnO nanoparticles as catalyst. The effects of sonolysis, sonocatalysis, photocatalysis and sonophotocatalysis have been examined to study the influences on the degradation rates by varying the initial dye concentration, dye solution pH, catalyst morphology and loading to ascertain the synergistic effect on the degradation techniques. ZnO sonophotocatalysis was always faster than the respective individual processes. Ultrasound may modify the rate of photocatalytic degradation by promoting the deaggregation of the catalyst and ultrasound-induced increase of its active surface area, by increasing the amount of reactive radical species through cavitation leading to water splitting and formation of H₂O₂ by both photocatalysis and sonolysis. To further verify the direct relation of the effective surface area offered by ZnO to its reaction rate, sonophotocatalysis experiments were conducted using nanorods of different dimensions and aspect ratios. Higher aspect ratio values correspond to an enhancement of the sonophotocatalytic activity.     

Response surface methodology applied for Orange II photocatalytic degradation in TiO2 aqueous suspensions

BACKGROUND: Heterogeneous photocatalysis is influenced by a number of parameters involving synergistic effects; hence, an experimental strategy design that considers interactions between the main variables is needed. The response surface methodology was applied for the investigation of photodegradation of 20 mg L^?1 Orange II in aqueous solutions and for optimization of color removal efficiency. Preliminary studies were performed to identify the parameters to be selected for optimization. RESULTS: The input variables considered for experimental design were: solution initial pH, oxidizing agent (H₂O₂) initial concentration and UV‐A irradiation time. The multivariate experimental design allowed the development of a quadratic response surface model to be used for the prediction of color removal efficiency over the full range of the experimental region. Under the optimum conditions established in the region of experimentation (pH = 6.9, [H₂O₂]₀ = 183 mg L^?1 and t = 32 min), a 100% color removal efficiency was obtained in experiments. CONCLUSIONS: It was found that the variables considered have important effects on color removal efficiency. The results demonstrate that the use of experimental design strategy is indispensable for successful investigation and adequate modeling of the process because the interdependence of the reaction parameters cannot be neglected. Copyright © 2008 Society of Chemical Industry     

光催化玻璃的生产与应用

介绍了光催化镀膜玻璃的工业性生产技术,测定了光催化薄膜对甲基橙的分解能力、通过薄膜的耐磨性测定,验证了薄膜在玻璃表面的附着强度。例举了光催化薄膜在使用上的特点。     

Degradation of Polyvinylpyrrolidone by Photocatalytic Ozonation and Evaluation of the Influence of Some Operational Parameters

Photocatalytic degradation of polyvinylpyrrolidone (PVP) by titanium dioxide and ozone in an annular reactor was investigated using a 125-W mercury vapor lamp as the light source. It was observed that the TiO₂/O₃/UV process presented a greater efficiency than the TiO₂/UV process. In fact, around 90% of the mineralization was obtained in 1 h of reaction, reflecting the synergistic effect of the combination of O₃ and TiO₂ under UV light, because the sum of the rate constants of the individual processes is less than the rate constant of the combined process. The effects of the initial PVP concentration, photocatalyst dosage, ozone input flow rate and pH on the PVP degradation rate were studied. In general, the results suggest that PVP can undergo a cross-linking process when the TiO₂/O₃/UV treatment is applied. The reaction rate was increased when the photocatalyst dosage was increased up to 2.0 g L^?1; however, increasing the initial PVP concentration led to a drop in the reaction rate. The efficiency also decreased at basic pH, because ozone is decomposed under alkaline conditions. In addition, it was noted that most of the nitrogen atoms of the macromolecules of PVP can be transformed into nitrate and ammonia during photocatalytic ozonation.     

Microbial cellulose as a support for photocatalytic oxidation of toluene using TiO2 nanoparticles

The aim of this study was to investigate the feasibility of toluene degradation using impregnated microbial cellulose (MC) with titanium dioxide (TiO₂) nanoparticles (MC/TiO₂). The effects of the initial toluene concentration and ultraviolet (UV) source on the degradation efficiency of toluene have been evaluated. The experimental results showed that the rate of toluene degradation decreased with an increasing of the inlet toluene concentration. After 40 min reaction time, the decomposition rate (%) of toluene decreased from 72.3% to 36.02% for experiments conducted at 100 and 500 ppm, respectively. The degradation efficiency of toluene decreased with application of UVA source instead of UVC source. The toluene degradation efficiency (%) reached to 87.79% and 76.87% for UVC and UVA irradiation, respectively. At initial toluene concentration of 100 mg/L, toluene degradation efficiency for photocatalysis and photolysis processes were 70.2% and 10.65%, respectively; indicating that the photocatalytic degradation efficiency is significantly higher than that of photolytic degradation efficiency. Furthermore, photocatalytic degradation kinetics of toluene was studied and the rates of degradation were found to conform to pseudo‐second‐order kinetic. As shown in the present study, impregnation of TiO₂ nanoparticles on MC/TiO₂ significantly increases toluene removal for short exposure time. It can be concluded that the MC acted as a local toluene concentrator by adsorbing pollutants from the air stream, and thereby diffusing them to the TiO₂ nanoparticles for photodegradation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43051.     

The combination of photocatalysis process (UV/TiO2(P25) and UV/ZnO) with activated sludge culture for the degradation of sulfamethazine

The major factors affecting the removal efficiency of sulfamethazine (SMT) by photocatalysis process in the presence of TiO₂ P25 or ZnO, namely the pH, the amount of catalyst and the initial SMT concentration were examined. The obtained results showed the absence of adsorption of SMT on the catalysts and the absence of degradation of SMT by direct photolysis under UV light in the absence of catalyst. The variation of the pH solution in the range 4–9 did not cause any significant degradation of SMT. The optimal amounts of each catalyst were, respectively, 0.5 and 0.25 g/L for TiO₂ P25 and ZnO. Increasing the initial SMT concentration impacted negatively the removal efficiency, which decreased from 31% to 13% and from 100% to 27% in the presence of TiO₂ P25 and ZnO in the presence of 10 mg/L and 50 of SMT after 30-min reaction time, respectively. The obtained results showed better efficiency of ZnO than TiO₂ P25 regarding both removal efficiency and chemical oxygen demand (COD) abatement. However, removal efficiency and COD abatement were not complete, even after 7 h of photocatalysis, about 92% and 41%, respectively. The biodegradability was examined after photocatalysis performed in the following conditions: [SMT]₀ = 50 mg/L, pH = 6, T = 25°C, ω = 360 rpm and 0.5 g/L of TiO₂ P25 or 0.25 g/L of ZnO. In these conditions, the removal efficiencies were, respectively, 26% and 41% in the presence of TiO₂ P25 and 55 and 92% in the presence of ZnO after 4 and 7 h of pretreatment times, respectively. The BOD₅/COD ratio increased substantially and, respectively, from 0 to 0.25 and from 0 to 0.16 in the presence of TiO₂ P25 and ZnO after 7 h of irradiation. Even if the limit of biodegradability (0.4) was not achieved, a subsequent biological treatment was considered in the presence of TiO₂ P25, leading to 58% COD abatement after a 28-day culture.     

Removal of organic contaminants in paper pulp effluents by AOPs: an economic study

The degradation of the organic content of a bleaching Kraft mill effluent was carried out using Advanced Oxidation Processes (AOPs). The study was focused on the identification of the AOP, or combination of AOPs, that showed the highest efficiency together with the lowest cost. Direct UV photolysis (UV), TiO₂ assisted‐photocatalysis (TiO₂/UV), Fenton, Fenton‐like, and photo‐Fenton reactions (Fe(II)/H₂O/UV), UV‐assisted ozonation (O₃/UV) and addition of Fe²⁺ and/or H₂O₂ to the TiO₂/UV and the O₃/UV systems, were used for the degradation of a conventional cellulose bleaching effluent. The effluent was characterized by the general parameters TOC, COD and color, and analyzed for chlorinated low molecular weight compounds using GC–MS. The costs of the systems per unit of TOC reduction were compared. Fenton, Fenton‐like and photo‐Fenton reactions achieved better levels of TOC degradation than photocatalysis and with lower cost's than photocatalytic treatments. Ozonation is an effective but rather expensive process. The use of UVA light, however, increased the effectiveness of ozonation with a significant decrease (>25%) in the operational cost. © 2002 Society of Chemical Industry     

Photoelectro-Fenton combined with photocatalytic process for degradation of an azo dye using supported TiO2 nanoparticles and carbon nanotube cathode: Neural network modeling

In this work, treatment of an azo dye solution containing C.I. Basic Red 46 (BR46) by photoelectro-Fenton (PEF) combined with photocatalytic process was studied. Carbon nanotube-polytetrafluoroethylene (CNT-PTFE) electrode was used as cathode. The investigated photocatalyst was TiO₂ nanoparticles (Degussa P25) having 80% anatase and 20% rutile, specific surface area (BET) 50 m²/g, and particle size 21 nm immobilized on glass plates. A comparison of electro-Fenton (EF), UV/TiO₂, PEF and PEF/TiO₂ processes for decolorization of BR46 solution was performed. Results showed that color removal follows the decreasing order: PEF/TiO₂ > PEF > EF > UV/TiO₂. The influence of the basic operational parameters such as initial pH of the solution, initial dye concentration, the size of anode, applied current, kind of ultraviolet (UV) light and initial Fe³⁺ concentration on the degradation efficiency of BR46 was studied. The mineralization of the dye was investigated by total organic carbon (TOC) measurements that showed 98.8% mineralization of 20 mg/l dye at 6 h using PEF/TiO₂ process. An artificial neural network (ANN) model was developed to predict the decolorization of BR46 solution. The findings indicated that artificial neural network provided reasonable predictive performance (R² = 0.986).     

Photocatalytic activity of transparent porous glass supported TiO2

A porous glass tube with a composition of 96SiO₂·4B₂O₃ (wt%) supported TiO₂ shows high photooxidation activity due to its transparency and large surface area. The surface area of the porous glass tube supported TiO₂ is 10,000 times larger than that of conventional materials. TiO₂ crystals supported are anatase type. Transparency of the porous glass tube is very important. Herein, sol–gel and chemical vapor deposition (CVD) processes were employed as TiO₂ supporting processes. CVD process is more effective. For instance, an aqueous methylene blue solution with 1 ppm concentration almost thoroughly decomposes at a contact time of 300 s using porous glass tube supported TiO₂ prepared by CVD process under irradiating with 10 W low-pressure mercury lamp, on the other hand, opaque porous alumina tube supported TiO₂ was only 25%. The smaller the pore size of the porous glass tube, the larger the transparency and the permeation resistance through porous glass tube. Hence, porous glass tube with ca. 40 nm pore diameter is suitable from the standpoint of a practical use.     

Influence of crystallization inside glass frit on seal stress in ceramic metal halide lamps

Ceramic metal halide lamps use polycrystalline aluminum oxide as an arc tube material; cracks inside the glass frit—used as the seal material—have been known to occur occasionally. This study measured the stress on the lamp seals caused by changes in the cooling rate during the sealing process by a 2D stress measurement method. Seal stress decreased with reducing cooling rate. Therefore, we discuss the influences of the glass frit's microstructure and the coefficients of thermal expansion (glass frit, capillary, and Nb wire) on the seal stress. The coefficient of thermal expansion of the annealed glass frit was essentially closer to those of the capillary and Nb wire, while that of the rapidly cooled glass frit differed greatly. Moreover, the glass frit of the rapidly cooled lamp seal contained only an amorphous phase (Dy, Si, Al, and O), while the glass frit of the annealed lamp seal contained both an amorphous phase (Dy, Si, Al, and O) and a crystalline one (Dy₂SiO₅ and Al₂O₃). Fracture toughness was found to be larger in the crystals than in the amorphous phase area. Moreover, it was larger in the area where crystalline Dy₂SiO₅ and Al₂O₃ were present compared to the area where only crystalline Dy₂SiO₅ was present.     

A novel photoelectrocatalytic system for organic contaminant degradation on a TiO2 nanotube (TNT)/Ti electrode

A novel degradation system, combined with photon-efficient thin-film photocatalysis, conventional bulk-phase photocatalysis and photocarrier-efficient electrocatalysis (TBPE), was developed on a vertically ordered one-dimensional (1D) TiO₂ nanotube (TNT)/Ti electrode for the purification of organics. The TBPE system possessed excellent optical, electrochemical, photoelectrochemical and photoelectrocatalytic properties as well as a high mass-transfer coefficient and interfacial activity. The combined degradation of methyl orange (MO) was optimized by varying the rotation angular velocity, applied bias and substrate concentration, and a photoelectrochemical synergetic effect of 62.2% was observed under the optimized conditions for TBPE compared to the individual electrocatalytic (EC) and photocatalytic (PC) systems. To explore the mechanisms, the combined thin-film degradation system of photon-efficient thin-film photocatalysis with photocarrier-efficient electrocatalysis (TPE), and the combined bulk-phase degradation system of conventional bulk-phase photocatalysis with photocarrier-efficient electrocatalysis (BPE), were comparatively estimated. A dramatic increase of 29.4-74.4% was observed in the MO removal efficiency via the thin-film TPE system compared to the bulk-phase BPE system. The results indicated that in the proposed TBPE system on the 1D TNT electrode, the predominant degradation occurred via the TPE system due to its excellent UV utilization efficiency and resultant interfacial photoactivity.     

微波辅助光催化降解4-氯酚的研究

采用了一种新的水处理技术微波辅助光催化(MW／UV／P25)降解4-氯酚(4CP)模拟废水。初始质量浓度为30mg/L的4CP在微波光催化下发生了降解,反应120min,4CP的降解率达到82．85％,Cl^-质量浓度增加值为7．95mg/L。4CP的降解率与溶液的pH、通气条件、紫外灯光照度等因素有关,外加H2O2氧化剂能够加速4CP的降解。微波辅助光催化降解4CP服从一级反应动力学方程。     

UV curing and matting of acrylate nanocomposite coatings by 172 nm excimer irradiation

For UV-curable acrylate coatings reinforced by silica nanoparticles, the effect of 172 nm excimer irradiation on the surface roughness has been studied. A dual UV lamp set-up consisting of a 172 nm excimer lamp and a mercury arc lamp allowed obtaining gloss levels down to 0.5 units (at 60°) depending on the acrylate formulation and curing conditions. Moreover, UV matt-finished sample showed enhanced surface hardness and increased chemical resistance. It is assumed that 172 nm excimer irradiation resulted in a higher network density via additional cross-linking reactions.To study the depth profile of acrylate conversion for coatings cured by the combination of a 172 nm excimer lamp (accountable for surface curing) and a mercury arc lamp (responsible for through curing), FTIR microscopy as well as (Ge)ATR-FTIR having an IR penetration depth of less than 0.5 μm have been applied. Providing the presence of a photoinitiator as well as the absence of oxygen inhibition, similar degrees of double bond conversion of about 90% were observed on the entire area of the cross-section of the coating, i.e. the wavelength of UV irradiation was found to have no significant impact on acrylate conversion.     

Photocatalytic membrane reactor for degradation of acid red B wastewater

Nano-titanium dioxide (TiO₂) photocatalyst was prepared by acid–sol method using tetrabutyl titanate and ethanol, which appeared to be anatase by XRD analysis. The wastewater containing azo dye acid red B was then subjected to photocatalytic degradation with photocatalyst TiO₂ and UV as light source in a slurry photocatalytic membrane reactor, which included a double layer cylindrical photocatalytic reaction zone and a plate frame membrane separation part. Two kinds of ultrafiltration (UF) membranes PVDF700 and PAN700 were applied and the combined process with photocatalysis was operated by a continuous re-circulating mode during treatment. At first, the adsorption characteristic of the titanium dioxide catalyst under different pH values was analyzed and the optimal operation condition of the photocatalytic process was achieved by changing TiO₂ dose and initial concentration of the dye. Then the performance of photocatalyst separation process by ultrafiltration (UF) was investigated. It was found that the degradation of acid red B was followed by first-order kinetics and the efficiency of photocatalysis can be evaluated by the initial reaction rate. Finally, the conglomeration and hydrophilizion phenomena by TiO₂ in the coupling system and its effect to different ultrafiltration membranes were analyzed.     

Enhancement of UV disinfection efficiency by arraying inclined lamps

A computational study on UV disinfection efficiency has been developed based on the Lambert-Beer law. Comparing a UV lamp arranged vertically to the flow of one arranged on an incline led to the conclusion that UV doses could be increased. The study of the inclination effect was divided into four stages in order to evaluate the increase in the UV dose at each stage. The slope of the inclined UV lamp ranged between 1‡ and 89‡ (0‡<θ<90‡) with other parameters such as diameter of the UV lamp, distance from the surface of the UV lamp, and velocity also recorded. The increase of UV dosage was largely affected by the diameter and velocity of the UV lamp, especially on a lesser slope. To obtain a greater UV dose, it was necessary to assemble UV lamps with lesser slopes. By arranging lamps on an incline, UV disinfection could be enhanced.