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Photocatalytic wastewater treatment is an affordable, low-cost, and environmentally friendly process that does not generate secondary waste. This review article categorizes challenges in photocatalytic wastewater treatment into two main areas: photoreactor design and photocatalyst synthesis. It specifically focuses on the proposed solutions by researchers, using ZnO photocatalyst as a case study. For this purpose, a comprehensive literature review was conducted to analyse the significant and impactful challenges in reactor design, photocatalytic reactions over photocatalysts, and scaling up the process. The obstacles existing in photoreactor design include light distribution, adverse effects of temperature increase, mass transfer limitations, photocatalyst separation from treated effluent, and recovery of photocatalyst. Strategies to overcome the challenges in photoreactor design include implementing new configurations of photoreactors, utilizing various substrate geometries, employing different light sources, etc. From a catalysis perspective, challenges include the wide bandgap of photocatalysts, electron-hole recombination, and mass transfer limitations within the photocatalyst cavities, insufficient adsorption of contaminants, the instability of certain photocatalysts under operating conditions, and minimal adsorption of photons by photocatalysts. This review article aims to contribute to enhancing the photocatalytic wastewater treatment efficiency in photodegradation of pollutants and scaling up its application as a primary method for wastewater treatment. The review indicates the influential role of photoreactor configuration on light distribution, the delivery of photons to the photocatalyst, and the generation of active species, thereby impacting process efficiency. Additionally, it reveals the impact of the physicochemical properties of the photocatalyst on the kinetics and mass transfer of the photocatalytic reaction. [ABSTRACT FROM AUTHOR]

Angina pectoris is chest pain that results from myocardial ischemia, or the temporary reduction in cardiac blood flow. Unstable angina is a rapidly deteriorating type of angina, caused in part by the formation of intracoronary thrombi (blood clots in the coronary arteries), that often presages the onset of more a more severe cardiovascular emergency such as heart attack. The long-term (for periods greater than six days) use of anticlotting drugs, such as heparin, is well established as a therapeutic strategy for the treatment of unstable angina. With current economic pressures to reduce the duration of hospital stays, it is of interest to know whether there is any therapeutic advantage to be gained by short-term intravenous administration of heparin. (The intravenous route of administration requires hospital care.) To determine the effect of short-term heparin administration on the frequency of ischemic events, a study was carried out involving 47 patients being treated for unstable angina. Twenty patients received intravenous heparin in addition to their other medications for the first 36 hours of evaluation; the remainder received an inactive saline (salt) solution in addition to the medications they had been taking. In both groups these medications included calcium channel blockers, beta adrenergic blocking agents, nitrates, and aspirin. Myocardial ischemia was monitored by electrophysiological monitoring of cardiac function. There was no difference in the frequency of ischemic events between the groups receiving heparin and saline. About 40 percent of both groups suffered ischemic episodes, the majority of which (85 percent) were asymptomatic. The failure of heparin to reduce the incidence of ischemia may be attributable to a masking effect of aspirin (which has much the same effect), the length of treatment, or the possibility that heparin might not exert its effects on angina solely by reducing myocardial ischemia. (Consumer Summary produced by Reliance Medical Information, Inc.)

In this paper, sol–gel technique with dip coating was used to prepare photocatalytic TiO 2 coatings on glass plates. Effect of different calcination temperatures of 400, 500, 600 and 700 °C on the photocatalytic activity of TiO 2 coatings was investigated in de-colorization of methylene blue under UV-A irradiations in a batch reactor. The highest methylene blue degradation was achieved by the coating calcined at 500 °C. Lower and higher calcination temperatures had lower activity in degradation of methylene blue. The TiO 2 coating calcined at 500 °C removed almost 90% of initial methylene blue while other coatings barley removed 30% of dye after 400 min of UV irradiations. XRD, FESEM, FTIR, EDX and TEM showed that the calcination temperature had a great influence on crystalline structure of TiO 2 coatings. The coating calcined at 400 °C indicated mixed phase of anatase and rutile but with increasing the calcination temperature to 500 °C, crystalline phase transformed from mixed phase to pure phase of anatase. The TiO 2 crystallites were small and highly dispersed in 500 °C calcined coating compared to other calcination temperatures. The sample calcined at 500 °C had a uniform morphology with smooth coating of small nanoparticles without any crack. Adhesion of TiO 2 coatings on glass plates was investigated by atomic absorption of treated wastewater and sonication weight loss of TiO 2 coatings. The amount of Ti leached from studied coatings was negligible and the 500 °C calcined coating showed the lowest weight loss after sonication. The effect of pH of wastewater, initial concentration of methylene blue and number of TiO 2 coated glass plates was evaluated in decolorization of methylene blue using the TiO 2 coating calcined at 500 °C. [ABSTRACT FROM AUTHOR]

In this study in order to create hydrophobic properties, hydrophobic silica aerogel were applied in various percentage. As can be seen from graphical abstract by adding 20% of hydrophobic silica aerogel, all particles become hydrophobic and float on water. Not only does silica aerogel give hydrophobic properties to Fe-ZnO, but also it was used as a support of catalyst in order to improve photocatalyst activity. Synthesized hydrophobic catalysis were used in degradation of BTX from wastewater. The results showed Fe-ZnO/SA (20%) composites depicted more photocatalytic activity than the rest of synthesized samples for degradation 5% V/V, so that the removal rate of 95.8% was made using 1 gr of Fe-ZnO/SA (20%) composite at pH=7 in 120 min. The reason for increased photocatalytic activity Fe-ZnO/SA (20%) composite can be said at the high surface area of Aerogel adsorbs more benzene and also with increase surface area, increase active sites in the photocatalyst composite, as a result, the adsorbed dyes are accessed in the active phase of composite and increased photocatalyst activity. Downward trend was seen in Fe-ZnO/SA (30%), it is due to adsorb excess contaminant by this composite, in line with this active phase of mentioned composite were poisoned and covered by benzene. [Display omitted] • Successfully synthesis floating Fe-ZnO/SA by precipitation impregnation method. • Giving hydrophobicity to Fe-ZnO/SA to decomposition of suspended BTX. • Formation of Fe-ZnO/SA (20) with high S BET 80.9 m2/g. • Proving the best synthesis method of floating Fe-ZnO/SA (20). • High photocatalytic activity of hydrophobic Fe-ZnO/SA (20) (95.8% BZ (5% V/V) decomposition in 120 min). Benzene, Toluene, and Xylene (BTX) are included in the floating contaminants which originated from the explosion of oil wells. Photocatalytic oxidation of the some oil spill components like Benzene, Toluene, and Xylene can be a proper way to solve this challenge due to its economic saving, usage of free energy, and environmentally friendly. For this purpose, we have synthesized a hydrophobic catalyst of Fe-ZnO nanoparticles inoculated with silica aerogel (SA). Various percentage of hydrophobic silica aerogel (10, 20 and 30%) was added, as support of catalyst, to Fe-ZnO nanoparticles using impregnation method. The impregnation of silica aerogel to Fe-ZnO nanoparticles caused the photocatalytic performance of nanocatalyst was improved through its increased surface area, and also floated active phase (Fe-ZnO) on water. In order to investigate the impact of the synthetic method of nanocomposite on the activity of synthesized nanophotocatalyst, optimum samples (Fe-ZnO over 20% SiO2) were synthesized using the sol-gel method. The synthesized nanophotocatalysts were characterized using PXRD, FESEM, EDX, UV–Vis, Contact Angle, FT-IR, and BET-BJH analyses. Photocatalytic activity of synthesized nanophotocatalyst was evaluated in the degradation of the BTX after 120 min, under visible light irradiation. In addition, the influence of various parameters including the addition of hydrophobic silica aerogel, pH, catalyst loading, benzene concentration, and reusability was studied on the photodegradation efficiency of Fe-ZnO/SA (20%). The most photocatalytic activity was observed in the optimum condition involving pH = 5, catalyst loading = 1 g/L, and benzene concentration = 5% V/V. [ABSTRACT FROM AUTHOR]

In this research, The Ag 2 CrO 4 over Silica Aerogel and Nano Silica was successfully synthesized using the precipitation method, which was used to obtain an appropriate morphology and used ultrasound to better particle distribution on Silica Aerogel and Nano Silica. To determine the physicochemical and optical properties of the synthesized samples, the characterization techniques such as XRD, FESEM, FTIR, BET-BJH, and UV–Vis DRS were employed. Photocatalytic experiments show that Ag 2 CrO 4 /NS(20%) has the highest solar-light-driven degradation of Acid Orange 7 (95.4% in 120 min). The best photo activity of Ag 2 CrO 4 /NS(20) is ascribed to efficient homogenous distribution of Ag 2 CrO 4 nanoparticles on the Nano Silica and Silica Aerogel, high surface area, and remarkable separation of charge carries and low recombination rate of electron-hole pairs due to the unique structure of Nano Silica. Also in this study Silica was synthesized by CO 2 reduction method to investigate the impact of surface area on photocatalyst performance of optimal sample (Ag 2 CrO 4 /NS(20)). As can be seen from FESEM images by adding Nano Silica more than 20%, agglomeration occurs. This agglomeration impedes Ag 2 CrO 4 Nano particles to adsorb light. [Display omitted] • Successfully synthesis Ag 2 CrO 4 over SiO 2 -Aerogel and Nano Silica by precipitation method. • Increase specific surface area of Ag 2 CrO 4 by applying Silica Aerogel and Nano Silica. • Optimum percentage of Nano Silica is 20%, more than this amount it cause to agglomeration on the surface of Photocatalyst. • Applying Nano Silica cause to reduce particle size and increase light adsorption on the surface of catalyst. In this study, Ag 2 CrO 4 /SiO 2 nanostructure was synthesized by the precipitation method to ameliorate the low specific surface area of Ag 2 CrO 4 with nano-Silica (NS) and Silica Aerogel (SA). The coupled nanophotocatalysts with various weighted contents of Ag 2 CrO 4 and Nano Silica were characterized with PXRD, FESEM, UV–Vis, FTIR and BET-BJH analyses. In order to find the optimal amount, different percentages of Nano Silica 10%, 20% and 30% were investigated. It was observed from BET-BJH that adding Nano Silica lead to an increase the catalyst surface area and crystallinity of synthesis samples. Then, in order to investigate the impact of specific surface area on optimal catalyst activity (Ag 2 CrO 4 /Nano Silica (20%)), Silica Aerogel, which has a higher surface area than Nano silica, was used instead of Nano silica. It was observed that increasing the surface area has a direct effect on the activity of the Ag 2 CrO 4. The photocatalytic activity of various nanocomposites was evaluated in the remediation of the organic dyes after 120 min visible light irradiation. The tremendous enhanced photocatalytic activity under the simulated solar light with 95.4% removal of AO7 was observed over Ag 2 CrO 4 /Nano Silica (20%) sample. In addition, to illustrate how the influence of various parameters such as various organic dyes, pH, catalyst loading and reusability on the photodegradation efficiency, were conducted over Ag 2 CrO 4 /Nano Silica (20). The high activity was obtained in the medium with pH = 7, catalyst loading = 1 g/L and AO7 concentration = 20 mg/L. [ABSTRACT FROM AUTHOR]