Solar Photocatalytic Processes Research Articles

TiO2–rGO nanocomposite as an efficient catalyst to photodegrade formalin in aquaculture's waters, under solar light

A solar photocatalytic process, using TiO2–rGO as photocatalyst, is proposed to degrade the formalin disinfectant. This process can treat aquaculture freshwater before its discharge or recirculation, promoting sustainable water.

Sonochemical-assisted route for synthesis of spherical shaped holmium vanadate nanocatalyst for polluted waste water treatment

Solar photocatalytic process has been shown to be an energy effective and eco-friendly degradation of unwanted pollutants present in the industrial wastewater. The present study introduces the preparation and characterization of novel holmium vanadate (HoVO4) nanostructures that fully used in the photodegradation efficiency of anionic and cationic organic pollutants. HoVO4 synthesized via a sonochemical-assisted route and triethylenetetramine (TETA) was used as a capping and precipitation agent. The experiments were carried out under a probe as sonication source, and its power was adjusted in 30 W (9 kHz), 50 W (15 kHz) and 80 W (24 kHz) for different samples. The obtained nanostructures were characterized by surface analytical and spectral techniques includes XRD, FT-IR, SEM, TEM and UV-visible spectra measurements. The HR-SEM images reveal that HoVO4 exists as a spindle-shape with spherical morphology together. HR-TEM images reveal that prepared catalyst has a spherical structure with uniform particle size. The results outline 67.6% elimination of methyl violet dye within 90 min under UV light in the presence of the optimal nano-sized formulation of 24.5 nm size. The prepared photocatalyst possesses high stability and reusability without appreciable loss of catalytic activity up to three runs.

Recent progress in MoS2 for solar energy conversion applications

In an era of graphene-based nanomaterials as the most widely studied two-dimensional (2D) materials for enhanced performance of devices and systems in solar energy conversion applications, molybdenum disulfide (MoS2) stands out as a promising alternative 2D material with excellent properties. This review first examined various methods for MoS2 synthesis. It, then, summarized the unique structure and properties of MoS2 nanosheets. Finally, it presented the latest advances in the use of MoS2 nanosheets for important solar energy applications, including solar thermal water purification, photocatalytic process, and photoelectrocatalytic process.

TiO2 3D structures for environmental purposes by additive manufacturing: Photoactivity test and reuse

From a technical point of view, currently, one of the most important problems to be solved in solar heterogeneous photocatalytic processes is related to the impractical use of the photocatalytic material in suspension form. In this study, we propose and develop 3D-printed hierarchical structures of entirely TiO2 consistency in order to investigate their effective photochemical and structural performance. Robocasting and deposition processes assisted the extrusion process through a syringe-type nozzle, dispensing, layer-by-layer, fine filaments of the catalytic paste and manufactured solid square-lattice double-diagonal (SLDD) structures. The concentration effect of SLDD solid pieces and nanopowder suspensions of TiO2 were compared for acesulfame (ACE) degradation as a model pollutant. 99% and 79% removal of 20 mg/L of ACE in solution were reached in 60 min of UV–Vis irradiation by use of 0.500 and 22 g/L of TiO2 in slurry and SLDD form, respectively. Long-term periods of use of SLDD pieces showed that the photocatalytic activity, pH and DO evolution remain unaltered after several cycles of reuse without macrostructure deformation or deterioration of the SLDD pieces. The optimal geometry of 3D printed structures of entirely TiO2 composition with optimum photonic flow distribution in solar reactors is a promising assignment to be achieved for the incoming commercial use of photocatalytic technologies at large scale for environmental sustainable applications.

Template free mild hydrothermal synthesis of core–shell Cu2O(Cu)@CuO visible light photocatalysts for N-acetyl-para-aminophenol degradation

Solar photocatalytic processes are a promising approach to environmental remediation, however their implementation requires improvements in visible light harvesting and conversion and a focus on low cost, Earth abundant materials.

Treatment of highly polluted industrial wastewater by means of sequential aerobic biological oxidation-ozone based AOPs

The feasibility of the treatment of a complex industrial wastewater by aerobic biodegradation in a sequential batch reactor (SBR) followed by ozone-based advanced oxidation processes (AOPs) has been studied. The industrial wastewater had high organic load (TOC > 3 g L−1, COD > 12 g L−1, BOD5 > 2 g L−1) including some toxic/harmful compounds and high concentration of metal and other inorganic species. SBR treatment of the industrial wastewater diluted with urban wastewater (dilution 1:5), was successful after complete acclimation of the mixed culture (i.e., >50% COD and TOC removals). Nevertheless, the SBR effluent was still not acceptable to be disposed into the environment (c.a. COD 850 mg L−1) so ozonation, solar photo-ozonation and solar photocatalytic ozonation processes were investigated as further polishing treatments. Thus, the sequential combination of aerobic biodegradation and solar photocatalytic ozonation with a TiO2-based catalyst led to an effluent suitable for discharge into the aquatic environment according to environmental regulations (COD < 125 mg L−1, BOD5 < 25 mg L−1).

Ho2WO6/ZnO nanoflakes for photo–electrochemical and self cleaning applications

Solar photocatalytic process has been shown to be an energy effective and ecofriendly degradation of unwanted pollutants present in the industry wastewater. In this study heterostructured 3 wt% Ho2WO6/ZnO was synthesized hydrothermally and characterised by surface analytical and spectral techniques. The HR–SEM images reveal that Ho2WO6/ZnO exists as nanoflakes with mesoporous microstructure clustered together. HR–TEM images reveal that prepared catalyst has hexagonal and spherical structure with uniform particle size. Ho2WO6/ZnO has more specific surface area (16.44 m2 g−1) than ZnO (11.80 m2 g−1). Reusable Ho2WO6/ZnO exhibited higher dye photodegradation efficiency, enhanced electrocatalytic activity by methanol oxidation and significant hydrophobicity.

Potential use of solar photocatalytic oxidation in removing emerging pharmaceuticals from wastewater: A pilot plant study

A pilot plant was used to evaluate the potential of solar photocatalytic processes in the treatment of wastewater containing emerging contaminates. Four groups of commonly used pharmaceuticals (antibiotics, estrogens, acidic, and neutral) were selected as model compounds and were treated with different combinations of solar advanced oxidation processes including solar-photolysis, homogenous solar oxidation with ferric ions, heterogeneous solar oxidation with titanium dioxide, and solar ozonation. Oxidation experiments were performed in Doha, Qatar (25.2854°N, 51.5310°E) under natural sunlight and at ambient temperature, in a semi-batch photo-reactor. Treatment performance was evaluated based on the efficiency of the processes in removing the target compounds and in mineralizing the organic content of the aqueous solution. The improvement in biodegradability and the reduction in the toxicity of the aqueous solution before and after the treatment were also evaluated. The results show that solar photolysis and solar oxidation with ferric ions are not effective in removing or mineralizing aqueous solutions containing the selected contaminates, while solar-driven oxidation processes with ferric ions, titanium dioxide, and ozone rapidly removed these pharmaceuticals from the wastewater and to some extent decreased the organic carbon content of the solutions. The removal efficiencies with solar photolysis and solar oxidation with ferric ions did not exceed 12.7% and 28.3%, respectively. Adding H2O2 to solar oxidation with ferric ions or utilizing TiO2 increased the percentage removal to the range 80–96%. Ozonation and solar ozonation processes removed 90–100% of the pharms in very short time. Performance indictor analysis showed that combining solar photocatalytic oxidation process with ozonation significantly improved the removal performance, increased the degree of mineralization, reduced the chemical requirements, and reduced the demand for ozone and energy. The kinetic profile of the combined processes is higher than that of the single oxidation process; thus, the combined oxidation processes is recommended for efficient treatment. The oxidation processes with their effective degradation capacity improved wastewater biodegradability and reduced its acute toxicity.

Study of solar photocatalytic degradation of Acesulfame K to limit the outpouring of artificial sweeteners

Abstract In this study, the photocatalytic degradation of an artificial sweetener, Acesulfame K (ACK), has been investigated with TiO2 photocatalyst using a solar simulator. Adsorption of ACK on TiO2 surface follows Freundlich adsorption isotherm in the pH range of 6–8 and shows an adsorption coefficient of 0.002 L/mg. Parametric studies for solar photocatalytic degradation are performed varying initial concentrations of ACK, photocatalyst dosage, and solar light intensity. Photocatalytic degradation rate of ACK gradually decreases with increasing initial concentration of ACK, and the rate follows pseudo first-order kinetics. The degradation rate of ACK gradually increases as the TiO2 dosage is increased and reaches maximum at 0.8–1.0 g/L. The rate constant for ACK degradation has been found to be directly proportional to light intensity, obeying a power law model. Complete degradation of ACK for 10–20 mg/L initial concentration is observed within the first 30 min of solar light irradiation of 100 mW/cm2 at pH 6. Complete mineralization of ACK can be achieved in 6 h with dissolved organic carbon (DOC) less than 1 mg/L. Complete mineralization of ACK and its by-products is successfully achieved with an apparent quantum yield of 0.02% at 1 sun thus making the process sustainable. This study manifests the efficacy of the solar photocatalytic process on degrading emerging pollutants like ACK where the use of artificial UV lamp has successfully been substituted by solar light, the most abundantly found sustainable source of energy in nature. Moreover, the process followed in this study is devoid of the use of any hazardous chemicals.

Lab scale optimization of various factors for photocatalytic hydrogen generation over low cost Cu0.02Ti0.98O2-δ photocatalyst under UV/Visible irradiation and sunlight

We have demonstrated earlier that maximum H2 generated @ 1.167 l/h/m2 over Cu0.02Ti0.98O2-δ photocatalyst with apparent quantum efficiency, AQE of 7.5% and solar fuel efficiency, SFE of 3.9% under sunlight. With an aim to scale-up the solar photocatalytic hydrogen process to pilot plant, optimization studies at lab scale as well as in upscaled photoreactors were performed over Cu0.02Ti0.98O2-δ, photocatalyst under UV/visible and sunlight. Cu0.02Ti0.98O2-δ was synthesized by facile sol-gel route and characterized by relevant techniques. Several operational parameters were investigated in order to finalize the conditions which are most favourable for photocatalytic hydrogen yield. Factors such as photocatalyst loadings, v/v concentration of sacrificial reagent, replacement of methanol by industrial waste glycerol, role of different configuration of light source with reactor, effect of stirring during the photocatalytic reaction, effect of fluctuations of solar flux at hourly basis, illumination area on hydrogen yield were studied. Contribution of each factor in determining the hydrogen yield was quantified. Relative standard deviation in hydrogen yield as a function of each factor was estimated. Our findings suggest that in addition to catalyst loadings and sacrificial reagent, improved dispersion of photocatalyst obtained by stirring the reaction mixture in horizontal geometry resulted in enhanced H2 yield. Hydrogen yield obtained at lab scale can be appropriately extrapolated with respect to illumination area instead of weight of photocatalyst. A relative standard deviation (RSD) of ± 3.82% and ± 4.53% in H2 yield was calculated for sunny and cloudy days in time zone of 10.30–16.30 h IST. Deviation of H2 yield was more on cloudy days and beyond 16:30 h. These studies have provided a daily window of 11:00–15:00 h to be utilized throughout the year for a commercial scaled up process, prohibiting the illumination during less productive hours of the day for shaping the improved economics of solar hydrogen generation. Our results obtained at lab scale would be useful to perform sunlight driven scaled –up photocatalytic process using low cost visible light efficient photocatalyst, Cu0.02Ti0.98O2-δ.

Hydrogen Generation through Solar Photocatalytic Processes: A Review of the Configuration and the Properties of Effective Metal-Based Semiconductor Nanomaterials

Photocatalytic water splitting and organic reforming based on nano-sized composites are gaining increasing interest due to the possibility of generating hydrogen by employing solar energy with low environmental impact. Although great efforts in developing materials ensuring high specific photoactivity have been recently recorded in the literature survey, the solar-to-hydrogen energy conversion efficiencies are currently still far from meeting the minimum requirements for real solar applications. This review aims at reporting the most significant results recently collected in the field of hydrogen generation through photocatalytic water splitting and organic reforming, with specific focus on metal-based semiconductor nanomaterials (e.g., metal oxides, metal (oxy)nitrides and metal (oxy)sulfides) used as photocatalysts under UVA or visible light irradiation. Recent developments for improving the photoefficiency for hydrogen generation of most used metal-based composites are pointed out. The main synthesis and operating variables affecting photocatalytic water splitting and organic reforming over metal-based nanocomposites are critically evaluated.

Ultraviolet and solar photocatalytic ozonation of municipal wastewater: Catalyst reuse, energy requirements and toxicity assessment

The present study evaluated the treatment of municipal wastewater containing phenol using solar and ultraviolet (UV) light photocatalytic ozonation processes to explore comparative performance. Important aspects such as catalyst reuse, mineralization of pollutants, energy requirements, and toxicity of treated wastewater which are crucial for practical implementation of the processes were explored. The activity of the photocatalysts did not change significantly even after three consecutive uses despite approximately 2% of the initial quantity of catalyst being lost in each run. Analysis of the change in average oxidation state (AOS) demonstrated the formation of more oxidized degradation products (ΔAOS values of 1.0–1.7) due to mineralization. The energy requirements were determined in terms of electrical energy per order (EEO) and the collector area per order (ACO). The EEO (kWh m−3 Order−1) values were 26.2 for ozonation, 38–47 for UV photocatalysis and 7–22 for UV photocatalytic ozonation processes. On the other hand, ACO (m2 m−3 order−1) values were 31–69 for solar photocatalysis and 8–13 for solar photocatalytic ozonation. Thus photocatalytic ozonation processes required less energy input compared to the individual processes. The cytotoxicity of the wastewater was analysed using the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay with Vero cells. The cell viability increased from 28.7% in untreated wastewater to 80% in treated wastewater; thus showing that the treated wastewater was less toxic. The effectiveness of photocatalytic ozonation, recovery and reusability of the photocatalysts, as well as detoxification of the wastewater make this low energy consumption process attractive for wastewater remediation.

Evaluation of synergy and bacterial regrowth in photocatalytic ozonation disinfection of municipal wastewater

The use of solar and ultraviolet titanium dioxide photocatalytic ozonation processes to inactivate waterborne pathogens (Escherichia coli, Salmonella species, Shigella species and Vibrio cholerae) in synthetic water and secondary municipal wastewater effluent is presented. The performance indicators were bacterial inactivation efficiency, post-disinfection regrowth and synergy effects (collaboration) between ozonation and photocatalysis (photocatalytic ozonation). Photocatalytic ozonation effectively inactivated the target bacteria and positive synergistic interactions were observed, leading to synergy indices (SI) of up to 1.86 indicating a performance much higher than that of ozonation and photocatalysis individually (SI≤1, no synergy; SI>1 shows synergy between the two processes). Furthermore, there was a substantial reduction in contact time required for complete bacterial inactivation by 50–75% compared to the individual unit processes of ozonation and photocatalysis. Moreover, no post-treatment bacterial regrowth after 24 and 48h in the dark was observed. Therefore, the combined processes overcame the limitations of the individual unit processes in terms of the suppression of bacterial reactivation and regrowth owing to the fact that bacterial cells were irreparably damaged. The treated wastewater satisfied the bacteriological requirements in treated wastewater for South Africa.

Performance of different photocatalytic oxidation processes in petroleum wastewater treatment: A Comparative Study

&lt;p&gt;The present study was conducted to compare the performance of different solar photocatalytic processes (TiO&lt;sub&gt;2&lt;/sub&gt; photocatalysis, photo-Fenton, photo-Fenton coupled with TiO&lt;sub&gt;2&lt;/sub&gt; photocatalysis, and photo-Fenton coupled with TiO&lt;sub&gt;2&lt;/sub&gt;/ZnO photocatalysis) for the treatment of petroleum wastewater. The removal efficiency of chemical oxygen demand (COD) is evaluated. TiO&lt;sub&gt;2&lt;/sub&gt; dosage and pH are the main factors that improve the COD removal in the TiO&lt;sub&gt;2&lt;/sub&gt; photocatalysis process while Fe&lt;sup&gt;+2&lt;/sup&gt; and H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; concentration are the main factors in photo-Fenton process. The photo-Fenton coupled with TiO&lt;sub&gt;2&lt;/sub&gt;/ZnO photocatalysis is the most efficient process for treatment of petroleum wastewater at the neutral conditions (pH 7). Therefore, no need to adjust pH during this treatment. In acidic conditions (pH&amp;lt;7), the photo-Fenton process is more efficient than the TiO&lt;sub&gt;2&lt;/sub&gt; photocatalysis process while it is less efficient than the TiO&lt;sub&gt;2&lt;/sub&gt; photocatalysis process in alkaline conditions (pH&amp;gt;7).&lt;/p&gt;

Enhanced Photodegradation of Phenol by ZnO Nanoparticles Synthesized through Sol-gel Method

Zinc oxide (ZnO) utilization in advanced oxidation process (AOP) via solar-photocatalytic process was a promising method for alternative treating wastewater containing phenol. The ZnO photocatalyst semiconductor was synthesized by sol-gel method. The morphology of the ZnO nanostructures was observed by using scanning electron microscope (SEM) and the crystallite phase of the ZnO was confirmed by x-ray diffraction (XRD). The objective of this study was to synthesis ZnO nanoparticles through a sol-gel method for application as a photocatalyst in the photodegradation of phenol under solar light irradiation. The photodegradation rate of phenol increased with the increasing of ZnO loading from 0.2 until 1.0 g. Only 2 h were required for synthesized ZnO to fully degrade the phenol. The synthesized ZnO are capable to totally degrade high initial concentration up until 45 mg L-1 within 6 h of reaction time. The photodegradation of phenol by ZnO are most favoured under the acidic condition (pH3) where the 100% removal achieved after 2 h of reaction. The mineralization of phenol was monitored through chemical oxygen demand (COD) reduction and 92.6% or removal was achieved. This study distinctly utilized natural sunlight as the sole sources of irradiation which safe, inexpensive; to initiate the photocatalyst for degradation of phenol.

Solar Photocatalytic of Reactive Blue Dye in Aqueous Suspension of V2O5

Decolorization of blue azo dye (Cibacron Blue FN-R) in simulated wastewater has been investigated as a function of solar photocatalytic process. Different parameters that affected on the removal efficiency, such as initial concentration of dye, pH of the solution, catalysis dosage, and H2O2 concentration, were evaluated to find the optimal operation conditions. From the experimental results, the desired pH value for solar photocatalytic V2O5 was 2 and the best catalysis dosage was 500mg/L. In addition, the most efficient H2O2 concentration was 100 mg/L for V2O5. The mathematical models that describe the photocatalytic process have been predicted by using response surface methodology (RSM). The decolorization efficiency by using V2O5 as solar photocatalytic can be reached to 97%.

An efficient pilot scale solar treatment method for dye industry effluent using nano-ZnO

Fabrication of photocatalysts and photoreactors for treatment of industrial effluents has become vital to harness solar energy for environmental cleanup. Treatment of dye industry effluent by heterogeneous photocatalysis with prepared nano ZnO in falling film photoreactor under natural solar light has been investigated. Different weight proportions of slurry comprising fevicol and homemade ZnO were prepared and the fevicol- ZnO (F-Z)film on acrylic sheet was obtained by brush coating. Coating of ZnO with 10wt% fevicol was found to be more adherent and efficient for dye degradation. This F-Z catalyst in the falling film photoreactor was tested for the treatment of dye effluent. F-Z catalyst prepared from nano-ZnO is more efficient than the catalysts made by commercial ZnO and TiO2-P25. The effects of operational parameters such as the amount of F-Z, effluent concentration, and initial pH on treatment process by F-Z coating as well as by suspended nano-ZnO slurry have been analyzed. Nano-ZnO is advantageous as its maximum efficiency occurs at neutral pH of 7. This pilot scale solar photocatalytic process can be widely applied at industrial scale.

Enhanced piezo/solar-photocatalytic activity of Ag/ZnO nanotetrapods arising from the coupling of surface plasmon resonance and piezophototronic effect

Ag/ZnO nanotetrapods are synthesized in mass production via a simple thermal-evaporation/hydrothermal route, and Ag nanoparticles are randomly coated on ZnO nanotetrapods. Ag/ZnO nanotetrapods can co-use the solar and mechanical energy to degrade various organic pollutants, and the solar-photocatalytic activity is significantly enhanced by the piezo-assistance. For instance, under ultrasonic stimulation (200W) and solar illumination (500W), Ag/ZnO nanotetrapods can completely degrade methyl orange (MO) within 25min. The high piezo/solar-photocatalytic efficiency of Ag/ZnO nanotetrapods can be ascribed to the coupling of surface plasmon resonance and piezophototronic effect in the solar-photocatalytic process. The localized surface plasmon resonance effect of Ag nanoparticles can increase the visible light absorption. Ag/ZnO interface can facilitate the interfacial charge transfer and induce the separation of photo-induced charge carriers. The piezoelectric field originated from the deformation of ZnO nanotetrapods can further enhance the separation of photo-induced electron/hole pairs. Our results imply that Ag/ZnO nanotetrapods have great potentials of using sustainable energy in the nature for environmental remediation.

Legionella jordanis inactivation in water by solar driven processes: EMA-qPCR versus culture-based analyses for new mechanistic insights

In this contribution, the validation of EMA-qPCR method for the quantification of viable Legionella spp. in water after solar treatments was carried out. EMA-qPCR was used to evaluate the different effects of several solar water disinfection processes over this bacterium, and furthermore their mode of action. Inactivation of Legionella jordanis in water by solar photocatalytic (TiO2 and TiO2/H2O2) and solar photochemical (solar/H2O2 and solar disinfection) processes have been investigated under natural sunlight. Culture-based and molecular (EMA-qPCR) techniques were systematically compared for the analysis of treated water samples. Solar tests were done under natural solar radiation (clear sky) and ambient temperature (20–35°C) for 2h, using H2O2/Solar (10, 20 and 50mg/L), TiO2/Solar (100, 200, 300, 400, and 500mg/L) and TiO2/H2O2/Solar (100/10, 200/10, 500/10mg/L). According to culture-based method, the best results of bacterial inactivation were obtained for 500/10mg/L of TiO2/H2O2. The order of efficiency to reach complete inactivation was: TiO2/H2O2/solar (5min)>TiO2/solar (15min)≈H2O2/solar (15min)>Solar only disinfection (90min). Moreover, EMA-qPCR and culturable counting results showed a direct correlation for samples treated with TiO2/solar for those catalyst concentrations that generate a strong oxidative attack over the cell wall. EMA-qPCR results demonstrated to be a good method to detect damaged and dead cells when the treatment affects the integrity of the cell’s membrane, as occurs under photocatalysis. Meanwhile for solar disinfection and solar/H2O2 (at non-toxic concentrations, <1.5mM), where membrane integrity remained unaltered, EMA-qPCR results couldn’t discriminate between alive and dead cells, even when the bacteria were not culturable.

Amoxicillin degradation from contaminated water by solar photocatalysis using response surface methodology (RSM)

In this study, the solar photocatalytic process in a pilot plant with compound parabolic collectors (CPCs) was performed for amoxicillin (AMX) degradation, an antibiotic widely used in the world. The response surface methodology (RSM) based on Box-Behnken statistical experiment design was used to optimize independent variables, namely TiO2 dosage, antibiotic initial concentration, and initial pH. The results showed that AMX degradation efficiency affected by positive or negative effect of variables and their interactions. The TiO2 dosage, pH, and interaction between AMX initial concentration and TiO2 dosage exhibited a synergistic effect, while the linear and quadratic term of AMX initial concentration and pH showed antagonistic effect in the process response. Response surface and contour plots were used to perform process optimization. The optimum conditions found in this regard were TiO2 dosage=1.5g/L, AMX initial concentration=17mg/L, and pH=9.5 for AMX degradation under 240min solar irradiation. The photocatalytic degradation of AMX after 34.95kJUV/L accumulated UV energy per liter of solution was 84.12% at the solar plant.