Artificial Solar Light Irradiation Research Articles

Synthesis of highly efficient (Cr, Gd) co-doped CdS quantum dots for photocatalytic H2 evolution beneath artificial solar light irradiation

To meet the future energy demand, the design, and development of novel, economical with efficient hydrogen (H2) fuel production rate and more stable photocatalytic material are most crucial and necessary. Numerous sunlight-active semiconductor nanostructures have been materialized for photocatalytic reactions towards hydrogen evolution. Nevertheless, their reliable application has been restricted through less photocatalytic efficiency and less stability provoked by the recombination of charge carriers. In the direction of to minimize the recombination rate among the charge carriers and enhance photocatalytic water splitting mechanism towards hydrogen evolution Co-doping of transition and rare earth elements to the host lattice is a promising strategy in functional material engineering to minimize the recombination rate among the charge carriers and enhance the photocatalytic water splitting mechanism towards hydrogen evaluation. In this view, herein, the chemical synthesis, structural, optical, and photocatalytic characteristics of pristine CdS, CdS:Cr (1 at%), CdS: (Cr, Gd (1 at%)) and CdS: (Cr, Gd (2 at%)) quantum dots for competent photocatalytic H2 fuel evolution. Furthermore, the rate of H2 of CdS: (Cr, Gd (2 at%)) quantum dots is almost 23 times greater than that of pristine CdS quantum dots with more stability. Hence, we strongly believe that, CdS: (Cr, Gd (2 at%)) quantum dots are reliable and potential semiconductor compounds for efficient photocatalytic hydrogen evolution for environmental purification.

Effect of atmosphere and relative humidity on photodegradation of clopidogrel under artificial solar and indoor light irradiation

Knowledge of the chemical stability of active pharmaceutical ingredients (APIs) is an important issue in the drug development process. This work describes a methodical approach and a comprehensive protocol for forced photodegradation studies of solid clopidogrel hydrogen sulfate (Clp) under artificial sunlight and indoor irradiation at different relative humidities (RHs) and atmospheres. The results showed that, at low RHs (up to 21%), this API was relatively resistant to simulated sunlight as well as indoor light. However, at higher RHs (between 52% and 100%), more degradation products were formed, and the degradation rate increased with rising RH. The influence of oxygen on the degradation was relatively low, and most degradation reactions proceeded even in humid argon atmosphere. The photodegradation products (DP) were analyzed with two different HPLC systems (LC-UV, LC-UV-MS) and selected impurities were separated by a semi-preparative HPLC and identified by high resolution mass spectrometry (ESI-TOF-MS) and 1H NMR techniques. Based on the obtained results, a light induced degradation pathway could be proposed for Clp in solid state.

Photocatalytic Inactivation of Co-Culture of E. coli and S. epidermidis Using APTES-Modified TiO2.

The presented work shows the antibacterial activity of TiO2 photocatalysts modified by 3-aminopropyltriethoxysilane (APTES). The APTES-functionalized TiO2 samples were obtained by the solvothermal process followed by calcination. The antibacterial activity of APTES/TiO2 samples was evaluated with two species of bacteria, Escherichia coli and Staphylococcus epidermidis, under artificial solar light (ASL) irradiation. The used bacteria are model organisms characterized by negative zeta potential (approx. -44.2 mV for E. coli and -42.3 mV for S. epidermidis). For the first time, the antibacterial properties of APTES-functionalized TiO2 were evaluated against mono- and co-cultured bacteria. The high antibacterial properties characterized the obtained APTES-modified nanomaterials. The best antibacterial properties were presented in the TiO2-4 h-120 °C-300 mM-Ar-300 °C sample (modified with 300 mM of APTES and calcined at 300 °C). The improvement of the antibacterial properties was attributed to a positive value of zeta potential, high surface area, and porous volume.

Impact of TiO2 Reduction and Cu Doping on Bacteria Inactivation under Artificial Solar Light Irradiation.

Preparation of TiO2 using the hydrothermal treatment in NH4OH solution and subsequent thermal heating at 500-700 °C in Ar was performed in order to introduce some titania surface defects. The highest amount of oxygen vacancies and Ti3+ surface defects were observed for a sample heat-treated at 500 °C. The presence of these surface defects enhanced photocatalytic properties of titania towards the deactivation of two bacteria species, E. coli and S. epidermidis, under artificial solar lamp irradiation. Further modification of TiO2 was targeted towards the doping of Cu species. Cu doping was realized through the impregnation of the titania surface by Cu species supplied from various copper salts in an aqueous solution and the subsequent heating at 500 °C in Ar. The following precursors were used as a source of Cu: CuSO4, CuNO3 or Cu(CH3COO)2. Cu doping was performed for raw TiO2 after a hydrothermal process with and without NH4OH addition. The obtained results indicate that Cu species were deposited on the titania surface defects in the case of reduced TiO2, but on the TiO2 without NH4OH modification, Cu species were attached through the titania adsorbed hydroxyl groups. Cu doping on TiO2 increased the absorption of light in the visible range. Rapid inactivation of E. coli within 30 min was obtained for the ammonia-reduced TiO2 heated at 500 °C and TiO2 doped with Cu from CuSO4 solution. Photocatalytic deactivation of S. epidermidis was greatly enhanced through Cu doping on TiO2. Impregnation of TiO2 with CuSO4 was the most effective for inactivation of both E. coli and S. epidermidis.

Synthesis and photocatalytic activity of bismuth carbonate micro-nanoplates

Vertically aligned faceted micro-nanoplates of bismuth carbonate (Bi2O2CO3) were successfully prepared by a free-surfactant/template hydrothermal method. The synthesized Bi2O2CO3 micro-nanostructures were characterized by XRD, FESEM, UV–vis absorption spectroscopy, and BET analysis. The photoactivity of Bi2O2CO3 micro-nanoplates were assessed using the organic pollutant crystal violet (CV) degradation under UV and artificial solar (AS) light irradiation. Electron transfer of Bi2O2CO3 was evaluated by photocurrent and EIS analysis. In addition, the possible growth and photodegradation mechanisms of the synthesized samples are briefly discussed.

The Benefits of Using Saccharose for Photocatalytic Water Disinfection.

In this work, the characteristics of saccharose (sucrose)-modified TiO2 (C/TiO2) photocatalysts obtained using a hydrothermal method at low temperature (100 °C) are presented. The influence of C/TiO2 on survivability and enzyme activity (catalase and superoxide dismutase) of Gram-negative bacteria Escherichia coli (ATCC 29425) and Gram-positive bacteria Staphylococcus epidermidis (ATCC 49461) under UV-A and artificial solar light (ASL) were examined. The obtained TiO2-1%-S-100 photocatalysts were capable of total E. coli and S. epidermidis inactivation under ASL irradiation in less than 1 h. In addition, the impacts of sugars on the photocatalytic activity and disinfection performance are discussed.

Influence of rGO and Preparation Method on the Physicochemical and Photocatalytic Properties of TiO2/Reduced Graphene Oxide Photocatalysts

In this study, a series of TiO2/rGO photocatalysts were obtained with a two-step procedure: a solvothermal method and calcination at 300–900 °C in an argon atmosphere. It was noted that the presence of rGO in photocatalysts had an important role in the changes in crystallite size and specific surface area. In TiO2/rGO samples, different surface functional groups, such as C−Cgraph, C−Caliph, C−OH, C=O, and CO(O), were found. It was observed that rGO modification suppressed the anatase-to-rutile phase transformation. The photocatalytic activity of the obtained nanomaterials was investigated through the decomposition of methylene blue under UV and artificial solar light irradiation. It was found that the adsorption degree played an important role in methylene blue decomposition. The experimental results revealed that TiO2/rGO samples exhibited superior removal efficiency after calcination for methylene blue compared toTiO2 without rGO, as well as a commercial photocatalyst KRONOClean 7000. It was noted that photocatalytic activity increased with the increase in the calcination temperature. The highest activity was observed for the sample calcined at 700 °C, which consisted of 76% anatase and 24% rutile. This study clearly demonstrated that TiO2/rGO samples calcined in argon can be used as efficient photocatalysts for the application of methylene blue decomposition.

Effect of APTES modified TiO2 on antioxidant enzymes activity secreted by Escherichia coli and Staphylococcus epidermidis

In this work, the impact of APTES-modified TiO2 photocatalysts on antioxidant enzymes (catalase and superoxide dismutase) activity secreted by bacteria was presented. Microbial tests has been examined using Escherichia coli (ATCC 29425) and Staphylococcus epidermidis (ATCC 49461) as model organisms. It was found that APTES-TiO2 affected the activity of antioxidant enzymes. Additionally, obtained APTES-TiO2 photocatalysts were capable of total E. coli and S. epidermidis inactivation under artificial solar light irradiation. The sample modified with the concentration of APTES equals 300 mM (TiO2–4h–120°C-300mM) showed the strongest photocatalytic activity toward both bacteria species. The two-stage photocatalytic mechanism of bacteria response to photocatalysts was proposed.

Synthesis of mixed oxide Ti/Fe2O3 as solar light-induced photocatalyst for heterogeneous photo-Fenton like process

Ti/Fe2O3 (Ti/Fe mass ratio ∼ 0.22) magnetic catalysts were prepared by a modified Pechini method and evaluated for heterogeneous photo-Fenton-like process for degradation of Reactive Black 5 (RB5) textile dye under artificial solar light irradiation. Catalysts were calcined at temperatures of 500–700 °C, and were characterized by TGA, XRD, N2 adsorption/desorption, FTIR, SEM, EDX and UV/Vis DRS analyses. The photo-Fenton experiments were conducted at pH 2.5, H2O2 initial concentration of 12 mmol L−1 and 0.40 g L−1 of catalyst. Results showed that catalyst calcined at 500 °C (TiFeO-500) achieved 100 % degradation of textile dye, the highest photoactivity, when compared with the materials calcined at either 600 or 700 °C and to the pure oxides α−Fe2O3 or TiO2, under the same conditions. Kinetic data related to RB5 dye degradation with TiFeO-500 catalyst was well fitted to the pseudo-first order model with initial reaction rate of 0.28 mg L−1 min−1. The high catalytic activity of this material was favored by its multiple bandgap from UV to visible range, as well as to its nanometric particle size and low agglomeration. Photoreduction efficiency of the Fe3+ to Fe2+ was favored by the synergy with Ti4+ and possible amorphous Fe and Ti oxysulfate species in the photo-Fenton like process for the production of hydroxyl radical (•OH) and dye degradation.

Influence of gadolinium (III) doping on the structural, optical, magnetic, and photocatalytic properties of CdS quantum dots

CdS, Cd0.98Gd0.02S, and Cd0.96Gd0.04S quantum dots (QDs) have been fabricated by solvothermal method and found to form in cubic phase. Raman spectra displayed first as well as second order longitudinal modes of CdS QDs. Transmission electron microscopy images depict the nearly spheroid particles of size in the range of 3.8–6.2 nm. Reflectance spectra showed that the absorption edge of the Cd0.98Gd0.02S and Cd0.96Gd0.04S QDs was red-shifted compared to that of CdS QDs. Electron paramagnetic resonance spectra of Cd0.98Gd0.02S and Cd0.96Gd0.04S reveal resonance signals at g ≈ 2.16 and 2.93 corresponding to the gadolinium (III) ions located at sites with frail as well as intermediate crystal field. Exploration of the magnetic property reveals that the Cd0.98Gd0.02S and Cd0.96Gd0.04S QDs show signs of superparamagnetism. The photocatalytic activity of CdS and Cd0.96Gd0.04S QDs was studied on malachite green oxalate dye under artificial solar light irradiation. The decomposition rate of CdS and Cd0.96Gd0.04S QDs evaluated on the malachite green oxalate dye is as follows: Cd0.96Gd0.04S > CdS.

Enhanced solar light driven activity of p-n heterojunction for water oxidation induced by deposition of Cu2O on Bi2O3 microplates

As an important half reaction in solar-driven water splitting, it is more challenging to develop low-cost and highly efficient photocatalysts for water oxidation. The enhancement of sunlight harvesting and inhibition of charge-carrier recombination are keys to fabricating efficient semiconductor-based photocatalysts for energy conversion from solar light to chemicals. Herein, we reported highly dispersive Cu2O/Bi2O3 composites prepared by a facile and benign synthetic route, where n-type Bi2O3 microplates and nano-sized p-type Cu2O were coupled together to construct heterojunctions to improve the transportation efficiency of photoinduced charge carriers, benefited from the intimate interactions at the interfaces between Bi2O3 and Cu2O. The electrochemical properties of charge-transportation and population of charge carriers were investigated in the heterojunctions. The hybrid materials exhibit both enhanced photocatalytic performances in water oxidation and photodegradation of dyes compared with sole Bi2O3 or Cu2O under artificial solar light irradiation. The initial O2 evolution rate of the heterojunction system is 1.4- and 8-fold higher than the pure Bi2O3 and Cu2O, respectively. This study provides new protocols for synthesizing novel hybrid materials with insights into heterojunction-based photocatalysis for green energy production and wastewater purification.

Natural solar light-driven preparation of plasmonic resonance-based alloy and core-shell catalyst for sustainable enhanced hydrogen production: Green approach and characterization

Plasmonic Co and/or Ag monometal and their combinations as bimetal alloy and core-shell nanoparticles were prepared under natural sun light, using aqueous glycerol (in-situ reducing agent) and TNP (stabilizer). The formation of bimetallic alloy and core-shell NPs, and their uniform dispersion on the surface of TNP were evidenced by different characterization techniques. Ultraviolet-visible diffuse reflectance spectroscopy evidenced the two distinct characteristic surface plasmon resonance (SPR) absorption bands for the core-shell nanoparticles and a single distinct characteristic SPR band for the alloy. X-ray photoelectron spectroscopy revealed the presence of Ag and Co in the metallic form. The results of H2-temperature programmed reduction of fresh and used samples emphasized the characteristic reduction peaks for the reduction of monometal/bimetal oxide to metallic/bimetallic particles. The interaction of the loaded bimetallic particles with TNP resulted in a shift in the Raman bands. The photoluminescence spectra of the used samples revealed the formation of bimetallic alloy and core-shell structures, which resulted in a decrease in the recombination of charge carriers. X-ray diffraction, electron paramagnetic resonance spectroscopy, high-resolution transmission electron microscopy, and cyclic voltammetry analyses substantiated the same. The monometal-loaded photocatalysts and the bimetal alloy and core-shell nanoparticle-loaded photocatalysts were further examined for H2 production with pure water/aqueous glycerol/crude glycerol under natural solar light irradiation. The (Ag-Co)coloadedTNP catalyst yielded the maximum H2 evolution rate of 63 mmol g−1. For comparison, experiments were conducted under artificial solar light irradiation with similar experimental conditions. Based on the results, different mechanistic paths for insitu photoreduced Ag-Co bimetallic alloy and core-shell nanoparticles on TNP for H2 production are envisaged.

Bioactive chitosan/ellagic acid films with UV-light protection for active food packaging

Homogeneous, translucent and flexible films of chitosan (CH) and ellagic acid (EA) were prepared by solvent casting. Various concentrations of EA (0.5, 1.0, 2.5 and 5.0% w/w relative to CH) were used in order to evaluate their UV-blocking properties. In addition, the photochemical stability of the films was also studied via artificial solar light irradiation. These set of films display high mechanical properties (Young’s modulus = 3.21–3.57 GPa), thermal stability up to 215–220 °C, UVA- and UVB-barrier properties, moderate water vapor permeability (WVP = 2.82–3.70 g mm m−2 day−1 kPa−1) and maximum antioxidant activity around 28% (DPPH scavenging activity). Furthermore, all CH/EA films show antimicrobial activity against food-borne pathogens such as Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacteria due to the CH antimicrobial effectiveness. These bioactive UV-blocking CH/EA films open the way to materials with potential for eco-friendly active packaging.

Experiment of water vapor adsorption/desorption rate in a desiccant rotor regenerated directly by concentrated artificial solar light irradiation

Experiment of water vapor adsorption/desorption rate in a desiccant rotor regenerated directly by concentrated artificial solar light irradiation

Titanium dioxide based nanotreatments to inhibit microalgal fouling on building stone surfaces

Stones are among the most widespread traditional materials used in construction for both structural and ornamental purposes, especially for Cultural Heritage monuments. Stone materials – both natural and man-made – are quite prone to algal colonisation that may cause biodeterioration of building materials by both affecting the aesthetic of their surfaces and compromising their entirety and durability. Nanotechnology has been recently used in both Cultural Heritage and construction industry to improve the preservation of building surfaces and titanium dioxide (TiO2) in its nanometric form is among the most used and promising nanotechnological material.This study investigated the biocidal ability of photocatalytic TiO2-based nanocompounds (also in combination with Ag and Cu nanoparticles) applied on travertine surfaces by spray-coating in order to limit or inhibit algal fouling. The aesthetic compatibility with stone has been assessed using colorimetry. Algal fouling was simulated by means of an accelerated water run-off test under artificial solar light and weak UV irradiation. Antialgal capability of metallic nanotreatments was evaluated through the combination of different parameters monitored for 9 weeks: human perception of the colour change, reflectance reduction and measurement of area colonised by algae. Nanoproducts had a limited impact on surface colour of the substrate after application making them suitable for restoration. Even though photocatalysis prevented algal fouling only partially, some nanotreatments moderately reduced the bioreceptivity of coated stones – mainly limiting the area colonised by microalgae. Further investigations are necessary, since the conditions used to accelerate algal growth may affect greatly the biocidal efficiency of nanotreatments.

A kinetic study of the simultaneous removal of EDDS and cupric ions from acidic aqueous solutions by TiO2-based photocatalysis under artificial solar light irradiation and deaerated batch conditions

The removal of cupric ions from aqueous solutions containing N,N′-ethylenediamine-disuccinic acid (EDDS) is carried out in batch conditions to simulate a possible treatment of water streams coming from soil washing treatment units for heavy metal decontamination. The reduction of cupric ions to zero-valent copper and the oxidation of EDDS species is observed with the achievement of low degrees of mineralization.A mathematical model has been developed to simulate and predict the concentration profiles of both total EDDS and cupric ions under specified experimental conditions. A series of experimental investigations have been carried out and the results have been used to build a reaction network. Kinetic models have been developed to describe the system behavior in a variety of operating starting conditions (such as different photocatalyst load, cupric ions and EDDS starting concentrations, pH). One of the mathematical models proposed has allowed to estimate the best numerical values of the unknown kinetic constants through an optimization process. A good alignment with the values reported in literature for similar reactions has also emerged for some kinetic constants. Model validation has been carried out successfully. The mathematical model proposed could be useful for the design of a photo-reactor, capable of purifying the solutions coming from soil washing procedure.

Low temperature one-step synthesis of rutile TiO2/BiOCl composites with enhanced photocatalytic activity

The rutile TiO2/BiOCl composites were successfully fabricated by a facile one-step hydrolysis method at low temperature (50°C). The X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–vis diffuse reflectance spectra, Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller, and X-ray photoelectron spectroscopy measurements were employed to characterize the phase structures, morphologies, optical properties, surface areas, and electronic state of the samples. The rutile TiO2/BiOCl composites exhibited higher photocatalytic activity than pure BiOCl and rutile TiO2 for the degradation of phenol under artificial solar light irradiation. In addition, the photocatalytic mechanism has also been investigated and discussed. The enhanced photocatalytic performance of rutile TiO2/BiOCl composites is closely related to the heterojunctions between BiOCl and rutile TiO2, which can not only broaden the light adsorption range of BiOCl but also improve the electron–hole separation efficiency under artificial solar light irradiation.

Preparation and photoelectric property of TiO2 nanoparticles with controllable phase junctions

To explore the effect of phase composition on the photoelectric property of anatase–rutile mixed crystal nanoparticles, a series of TiO2 nanoparticles with phase junctions controlling were synthetized by hydrolysis of TiCl4 in hydrochloric acid, an ionic liquid-assisted method was used during this process. Crystalline size and the ratio of anatase to rutile of as-prepared samples were calculated by the XRD. The surface area was measured by nitrogen sorption measurements using the BET method. The micro-structure of phase junctions was characterized by TEM. Optical transmittance properties of TiO2 with controllable phase junctions were examined via ultraviolet–visible diffuse reflection spectroscopy (UV–vis DRS). The particles were manufactured into films using the doctor-blade technique on FTO glasses. To test photocurrent density, and spatial separation capacity of electron–holes pairs, photo-electro method was employed. The photocatalytic activities of the resulting samples were examined in the degradation of methyl orange (MO) under artificial solar light irradiation. Mechanisms of separation and transfer of photogenerated charge and the effect of phase composition on photoelectric property of anatase–rutile nanoparticles were discussed.

Template-free synthesis of TiO2 microcages in agarose gels with improved photocatalytic activity

A template-free synthesis of TiO2 microcages by using (NH4)2TiF6 and NaOH as the reactants and the agarose gel as the reaction medium is developed. The resultant TiO2 microcages possess a pseudo-cubic morphology with the edge size of 1–2 μm and the shell thickness around 48 nm. It is found that the shell of TiO2 microcages consists of anatase TiO2 nanoparticles about 15 nm in diameter, and possesses the mesopores about 3.8 nm in size. A proposed formation mechanism suggests that pseudo-cubic Na5Ti3F14 microcages firstly generate in agarose gels due to the incomplete hydrolysis of TiF6 2− and the inhibited diffusion effect of gels, and then transform into anatase TiO2 without changing the morphology as the agarose gels are removed in hot water about 90 °C. These TiO2 microcage samples exhibit higher photocatalytic activity than Degussa P25 for the degradation of methyl orange under artificial solar light irradiation, which can be attributed to their well-preserved hollow structure with mesopores. This study may devote a novel and facile approach for the template-free synthesis of hollow structure functional materials.

Bio-inspired synthesis of TiO2 hollow nanospheres in agarose gels

TiO2 hollow nanospheres have been synthesized in agarose gels by a bio-inspired method for the first time in this study. Their outer and inner diameter are about 99.7 and 56.8nm, respectively, and their shell has bimodal mesopores about 3.8 and 5.5nm in size. These mesopores may be formed through removing the agarose gel fibers embedded in the shell of TiO2 hollow nanospheres during their nucleation and growth. It is inferred that a spherical composite formed by protamine and agarose molecules takes a key role in the formation of TiO2 hollow nanospheres. After calcined at high temperature (400–600°C) for 2h, these TiO2 materials exhibit higher photocatalytic activity for the methyl orange decoloration than Degussa P25 under artificial solar light irradiation. This study may provide a novel and facile approach for the synthesis of metal oxide hollow nanospheres under mild conditions.