Visible-light Activity Research Articles

Visible light active Bismuth ferrite embedded TiO2 nanocomposite structures for dye mineralization by photocatalysis -A strategy to harness solar energy for remediation of water contaminated with mixture of dyes

Harnessing solar energy to treat effluents from industries in order to mineralize the organic pollutants by photocatalysis demands the use of photocatalysts which are visible light active. In the present study, Bismuth ferrite embedded TiO2 (BFO/TiO2) nanocomposites have been synthesized with BFO (prepared by co-precipitation method) to Ti molar ratio of 1:2. BFO/TiO2 nanocomposites are crystalline, oval shaped and monodispersed with the average hydrodynamic diameter of 42 nm. Transmission Electron Microscopy (TEM) revealed that BFO nanoparticles have an average shorter dimension of 13.4 nm and longer dimension of 15.5 nm and are embedded in TiO2 matrix with the average coating thickness of 4.8 nm. The apparent band gap energy of BFO/TiO2 is 1.8 eV. BFO/TiO2 nanocomposites were used for the degradation of dyes from mixed dye aqueous solution containing three azo dyes, viz. Methylene Blue (MB), Acid yellow-17 (AY- 17), and Rhodamine- B (Rh-B) dyes under visible light irradiation. The BFO/TiO2 nanocomposites exhibited good photocatalytic activity under visible and solar light. Around 92% of MB, 73.9% of AY-17 and 68.3% of Rh-B dyes were degraded in 210 min from the mixed dye aqueous solution. Chemical Oxygen Demand (COD) removal of 72% could be achieved by photocatalysis confirming the mineralization of dyes. The COD removal kinetics followed first order model with the rate constant of 0.006 min−1. BFO/TiO2 nanocomposites exhibited superior visible light activity compared to BFO or TiO2 (Degussa P25) nanoparticles. The BFO/TiO2 nanocomposites have been proven to be promising in remediation of wastewater contaminated with mixture of dyes by photocatalysis.

Single-colour, visible light activation and excitation of the luminescence of a ‘switch-on’ dye and enhancement by silver nanoparticles

We synthesized a fluorogenic methylated dihydrofluorescein derivative in two convenient steps from commercial fluorescein. This species can switch to the corresponding oxidized form upon visible-light illumination at an activating wavelength of 455 nm, where the photoinduced transformation culminates in the activation (‘switch on’) of the fluorescence, which can be observed by exciting the photoproduct at the same wavelength of activation. Thus, a single wavelength can be used to simultaneously activate and excite fluorescence. Mechanistic investigations suggest that singlet oxygen does not contribute to the formation of the fluorescent oxidation product. The single-colour activation/excitation mode of this model structure can effectively mimic a pseudo two-colour system and can find broad application in the development of photonic materials operated with simple optical setups. The activated fluorescence can be concomitantly enhanced by triangular silver nanoparticles according to the principles of metal-enhanced fluorescence (MEF).

Interlayer Charge Transfer Over Graphitized Carbon Nitride Enabling Highly-Efficient Photocatalytic Nitrogen Fixation.

Exploiting cost-effective, high-efficiency, and contamination-free semiconductors for photocatalytic nitrogen reduction reaction (N2 RR) is still a great challenge, especially in sacrificial-free system. On basis of the electron "acceptance-donation" concept, a boron-doped and carbon-deficient g-C3 N4 (Bx CvN)isherein developed through precise dopant and defect engineering. The optimized B15 CvN exhibisted an NH3 production rate of 135.3µmolh-1 g-1 in pure water with nine-fold enhancement to the pristine graphitic carbon nitride (g-C3 N4 ), on account of the markedly elevated visible-light harvesting, N2 activation, and multi-directional photoinduced carriers transfer. The decorated B atoms with coexistent occupied and empty sp3 hybridized orbitals are theoretically proved to be in charge of the increase of N2 adsorption energy from -0.08 to -0.26eV and the change in N2 adsorption model from one-way to two-way end-on pattern. Noticeably, the elaborate coordination of doped B atoms and carbon vacancies greatly facilitated the interlayer interaction and vertical charge migration of Bx CvN, whichisdistinctly revealed through the charge density difference calculations. The current study provides an alternative groundbreaking perspective for advancing photocatalytic N2 RR through the targeted configuration of the defect and dopant sites.

Conducting polymer based visible light photocatalytic composites for pollutant removal: Progress and prospects

Conducting polymers (CPs) have been proved to be instrumental in enhancing photocatalytic efficacy owing to their unique physicochemical properties and energy levels. In this regard, titanium dioxide (TiO 2 ) has been investigated in transdisciplinary research areas (like catalysis, energy technologies, health, and environment) due to its desirable characteristics. In the process of developing advanced photocatalysts, novel inorganic–organic heterojunction design based materials have been explored and developed in contrast to conventional, inorganic–inorganic type semiconducting photocatalysts (SCPs). In this context, hybrid/composite SCPs comprising CPs and TiO 2 , have received significant attention for enhancing photocatalytic efficacy in terms of activity as well as visible light activation. The synergistic contribution from CPs (here we focus only on polyaniline (PANI) and polypyrrole (PPy)) and TiO 2 have been proved to enhance light-absorption capability in the visible region, photogenerated extraction, and higher stability. Importantly, the published literature (before 2015) on the photocatalysis of TiO 2 -CP composites mainly discusses in terms of the sensitizing aspects of CP for TiO 2 . However, there is a critical need to review the literature (beyond 2015) to explore the state of art progress concerning the mechanism of photocatalytic performances as phenomenal parallel developments and knowledge gaps have been addressed on new kinds of heterojunction formation (like S-Scheme over traditional ones), band tuning and interfacial contact effects between two SCPs. In particular, this topical review aims to capture and highlight the current advancements (2016–2021) in relevance to the visible light photocatalytic performance of CP–TiO 2 functional composites, which include nanostructures and multi-components. The predominantly available literature over the last five years on the application of CPs–TiO 2 functional composites for monitoring or removal of pollutants under visible light activation is reviewed giving importance to revealing the role of CP in concurrent enhancement in both visible light activation and photocatalytic performances. Finally, we elaborate on the challenges and future outlook for advanced research and development in this area. • Captured the recent advances in hybrid conducting polymer functional composites. • Discussed the role of conducting polymer in visible light-mediated photocatalysis. • Reviewed various types of nanocomposites photocatalysts for pollutant removal. • Synergistic contributions and importance of these hybrid composites were elaborated.

Efficient visible light activities of Ag modified ZnO/g-C3N4 composite for CO2 conversion

• Designing unique system based on Ag/ZnO/g-C 3 N 4 . • Charge separation and transfer mechanism discussion. • Photocatalytic CO 2 conversion to CO/CH4. Methane and CO have superior economic value and application panorama compared with other products, and these are the ideal products of CO 2 photo-reduction. However, low CO 2 conversion efficiency and poor selectivity are huge obstacles to its practical application. Herein, we develop a three-component photocatalyst hetero-junction of Ag-ZnO/g-C 3 N 4 for superior CO 2 reduction. It is demonstrated that the amount-optimized nanocomposite exhibited exceptional visible-light photoactivities for CO 2 conversion to CO, with ≈ 9-time (36 µmol g −1 h −1 ) enhancement compared to the widely accepted g-C 3 N 4 prepared from melamine as the raw material. Similarly, the silver-modified samples exhibit a considerable increase in methane production, with 14 µmol g −1 h −1 , which is significantly more than the CH 4 production of 2 µmol g −1 h −1 by pure g-C 3 N 4 . Based on the photo-physical data, it is concluded that the coupled ZnO, which accepts electrons and improves reactant adsorption, and the modified Ag, which further promotes the photocatalytic reaction, are much more responsible for the high photoactivities. Moreover, it is suggested based on the photocatalytic experiments with isotopic 13 CO 2 that the produced • CO 2 as active radicals dominated the conversion of CO 2 to CO/CH 4 . This work provides a feasible strategy to design high-performance, low-cost, and sustainable g-C 3 N 4 -based nanocomposite photo-catalysts with a wide range of visible light activity for CO 2 reduction.

Ternary silver tungstate-MoS2/graphene oxide heterostructure nanocomposite for enhanced photocatalysis under visible light and antibacterial activity

Wastewater emanating out of industrial units is loaded with hazardous organic dyes. The hindrance in sunlight penetration into the water by this dye-loaded wastewater has led to disruption in an aquatic ecosystem. Along with these carcinogenic pollutants, biological pollutants such as noxious bacteria are present in wastewater posing serious health problems. Fabrication of narrow bandgap visible light active photocatalysts is crucial these days. Metal tungstates and metal sulphides are mainly being sought due to their unique tailorable optical and chemical properties. In the present study, silver tungstate-MoS2 supported on graphene oxide was synthesized utilizing the ultrasonic-assisted hydrothermal method. The as-synthesized ternary nanocomposite was characterized by XRD, FTIR, SEM-EDS, TEM, XPS, BET, PL, and UV-vis techniques. The photocatalytic activity of prepared nanocomposites was evaluated using methyl orange degradation under visible light. The ternary nanocomposite showed improved photoefficiency, attaining 93 % methyl orange degradation in 90 min under various optimized conditions of solution pH = 5, initial dye concentration of 10 ppm, and catalyst dose of 50 mg/100 ml. The modelization and optimization for assessing the interaction effect amongst several variables were evaluated employing Response Surface Methodology (RSM). The antibacterial activity of synthesized binary and ternary hybrid nanocomposites was determined by the inactivation of gram-negative (Escherichia coli) and gram-positive (Staphylococcus aureus) bacteria. The improved photocatalytic and antimicrobial activities of ternary nanocomposite may be credited to the synergistic effect of heterojunction among three components.

Fabrication of novel BiVO4/Bi2O3 heterostructure with superior visible light induced photocatalytic properties

Heterostructure BiVO4/Bi2O3 nanocomposites with enhanced visible light activity are effectively synthesized through an easiest and single step hydrothermal route, using bismuth subnitrate and ammonium meta-vanadate as main raw materials in existence of citric acid. The phase and surface structure, topography and optical properties of synthesized composites are characterized by XRD, SEM, EDX, FTIR, UV–Visible and PL spectroscopy. It was found that 5%BiVO4/Bi2O3 (BOBV-5) nanocomposite exhibit excellent photocatalytic performance for rhodamine B dye degradation and tetracyclic under irradiation of visible light as compared to single component i.e. BiVO4. The increased photocatalytic activity should be ascribed for making p–n heterojunction among p-type Bi2O3 and n-type BiVO4. This p–n heterojunction successfully reduce the recombination of photogenerated charge carriers. Furthermore, the BOBV-5 novel photocatalyst shows good stability in constructive five cycles and photocatalytic activity is best for conquering photo corrosion of a photocatalysts. To explain charge migration route, whole photocatalytic mechanism was described in terms of energy band structures. Furthermore, the present work is helpful effort for design of new visible light photocatalytic materials with heterojunction structures.

Visible light irradiated photocatalytic reduction of CO2 to hydrocarbons using hybrid polyaniline/ CuO nanocomposite in aqueous system

ABSTRACT The ever-increasing energy demand has resulted in an increase in CO2 emissions and global warming. Photocatalytic reduction of CO2 to methanol, which is considered to be the next generation alternate fuel is gaining interest to combat global warming and to move towards a methanol economy. The present work focuses on photocatalytic reduction of CO2 using Polyaniline/CuO (PANI/CuO) nanocomposite to methanol, formic acid, and formaldehyde under visible light irradiation. CuO nanoparticles were synthesised using the aqueous extract of Tectona grandis (teak) leaves and further used in the synthesis of PANI/CuO nanocomposite with different CuO loading. PANI/CuO nanocomposite exhibited visible light activity in the reduction of CO2 to form methanol, formic acid, and formaldehyde. Photocatalytic reduction of CO2 with PANI/CuO nanocomposite containing 13.7% by weight of CuO resulted in a maximum yield of methanol. The band gap energy of the nanocomposite was found to be 2.28 eV, thus confirming its good visible light activity and the PANI-CuO heterojunction-based mechanism of photocatalysis is proposed. The synthesis of PANI-CuO photocatalyst uses CuO which is synthesised by an eco-friendly route with the utilisation of teak leaves, a timber industry waste and thus it can serve as a greener catalyst.

Chlorophyll sensitized and salicylic acid functionalized TiO2 nanoparticles as a stable and efficient catalyst for the photocatalytic degradation of ciprofloxacin with visible light

Developing efficient and stable visible light active photocatalyst has significant environmental applications. Though dye sensitization of TiO2 nanoparticles with natural chlorophyll pigments can potentially impart visible light activity, their long-term stability is a major concern. We investigated the functionalization of TiO2 with salicylic acid, and subsequent sensitization with chlorophylls to improve the catalyst stability for the photocatalytic degradation of Ciprofloxacin (CPX) under visible light. A significant improvement in the degradation efficiency and catalyst stability was observed for five reuse cycles. Further, an optimum CPX degradation of ∼75% was achieved with 0.75 g L−1 catalyst dosage of 0.1 chl/0.1 SA-TiO2, initial pH of 6, and 10 ppm of initial CPX for a visible light exposure of 2 h. The degradation followed the pseudo-second-order kinetics. In addition, the ciprofloxacin degradation was reduced in the wastewater matrix system due to the presence of other scavenging species such as chlorides, sulphates, and alkalinity. Significant reduction in the toxicity of degradation compounds after the photocatalytic degradation was observed in comparison to parent CPX. Further, the degradation pathway and plausible mechanism of degradation of CPX were also proposed.

Efficient Visible-Light Activities of TiO2 decorated and Cr3+incorporated-porous SmFeO3 for CO2 conversion and 4-chlorophenol degradation

In this novel research work, Cr3+ incorporated and TiO2-modified porous SmFeO3-based nanocomposites are prepared via utilizing carbon nanosphere (CNS) as a hard template. Our experimental results proved that the introduction of porosity by employing a sequential template approach (STA) has upgraded the performances of SmFeO3 nanoparticles. Remarkably, the incorporation of Cr3+ increased the light absorption capability by generating surface states and regulating band gap positions, whereas the fabrication of TiO2 enlarged surface area and enhanced charge separation by modulating high-level energy electrons (HLEEs). According to our experimental techniques, including TEM, HRTEM, SEM, TGA, BET, PEC, FS, and PL, it is demonstrated that most optimal 6Cr-PSFO and 4TiO2/6Cr-PSFO nanocomposites have high porosity, appropriate bandgap positions, large surface area, and show superior visible-light photocatalytic activities compared to pristine SmFeO3 nanoparticles. Compared to pristine SFO, the activities of most active 4TiO2/6Cr-PSFO nanocomposites are improved by 8-fold for CO2 conversion and 3-times for 4-chlorophenol (4-CP) degradation. The radical trapping experiment confirmed that the ·OH i are the most active species and has a vital role in the photocatalytic degradation of 4-CP. Moreover, our experimental results are verified and consistent with theoretical calculations and computational studies. Finally, our research work will open up a new gateway for the designing of novel porous SmFeO3-based nanocomposites and their use in CO2 conversion and pollutant removal.

Large-scale synthesis of visible light responsive ZnS by one-step molten salt method

It still remains a big challenge for the large-scale synthesis of visible light responsive ZnS. In this work, a simple one-step molten salt method is developed for large-scale synthesis of visible light responsive ZnS, in which the as-obtained sample at T oC is named as ST (T = 200, 300, 400, 500, 600 °C). The degradation reaction of Rhodamine B (RhB) is used to evaluate photocatalytic activity under visible light (λ ＞ 400 nm). Among the samples, S200 shows the highest visible light activity. Under visible light irradiation (λ ＞ 400 nm), 70% of RhB can be degraded by S200 after 90 min. Typically, the visible light activity of S200 is 28.2 times higher than that of S600. The higher activity of S200 is mainly attributed to more sulfur vacancies (VS), wider light absorption range, higher charge separation efficiency and larger BET area. Specifically, the BET area of S200 (44.4 m2 g−1) is 4.1 times higher than that of S600 (8.7 m2 g−1), thus S200 can provide more active sites. Meanwhile, the photocurrent for S200 is 6 times higher than that of S600, demonstrating that S200 has a higher charge separation efficiency mainly caused by more surface VS. Density functional theory (DFT) calculation further demonstrates that VS is favorable thermodynamically for the adsorptions of O2 and H2O, which benefits the generation of •OH and •O2– active species, leading to an improved activity. After three cycles of RhB degradation, S200 shows outstanding stability with 95% visible-light activity remained. The molten salt method is simple and productive, which can be used for large-scale synthesis of photocatalysts in practice.

Visible-Light-Driven Photocatalysts for Self-Cleaning Transparent Surfaces.

Highly transparent photocatalytic self-cleaning surfaces capable of harvesting near-visible (365-430 nm) photons were synthesized and characterized. This helps to address a current research gap in self-cleaning surfaces, in which photocatalytic coatings that exhibit activity at wavelengths longer than ultraviolet (UV) generally have poor optical transparency, because of broadband scattering and the attenuation of visible light. In this work, the wavelength-dependent photocatalytic activity of Pt-modified TiO2 (Pt-TiO2) particles was characterized, which exhibited activity for wavelengths up to 430 nm. Pt-TiO2 nanoparticles were embedded in a mesoporous SiO2 sol-gel matrix, forming a superhydrophilic surface that allowed for water adsorption and formation of reactive oxide species upon illumination, resulting in the removal of organic surface contaminants. These self-cleaning surfaces only interact strongly with near-visible light (∼365-430 nm), as characterized by photocatalytic self-cleaning tests. Broadband visible transparency was preserved by generating a morphology composed of small clusters of Pt-TiO2 surrounded by a matrix of SiO2, which limited diffuse visible light scattering and attenuation. The wavelength-dependent self-cleaning rate by the films was quantified using stearic acid degradation under both monochromatic and AM1.5G spectral illumination. By varying the film morphology, the average transmittance relative to bare glass can be tuned from ∼93%-99%, and the self-cleaning rate can be adjusted by more than an order of magnitude. Overall, the ability to utilize photocatalysts with tunable visible light activity, while maintaining broadband transparency, can enable the use of photocatalytic self-cleaning surfaces for applications where UV illumination is limited, such as touchscreen displays.

Photocatalytic activity of electrospun Fe‐doped ZnO nanofibers: Synthesis, characterization and applications

AbstractFe‐doped ZnO ceramic nanofibers (CNFs) as specific structural features and unique properties synthesized by using electrospun technology. X‐ray diffraction disclosed the wurtzite phase, and the microscopy analysis by SEM revealed the formation uniform nanofibers with 400 nm in diameter. The UV–visible diffuse reflectance spectroscopy (DRS) was used to investigation the optical properties of the pristine and the various percentages Fe doped ZnO photocrystalysts. The photo‐reduction activities of photocatalyst were evaluated using methylene blue (MB) as organic contaminant irradiated with simulate solar light from xenon lamp. The photocatalytic results that 1% Fe‐doped ZnO CNFs exhibits efficient visible and UV light activity and excellent photo‐stability. The kinetic constant of MB degradation over 1% Fe‐doped ZnO is about 2.2 times higher than that over pure ZnO. The experiment demonstrated that the photodegradation efficiency of Fe‐doped ZnO was significantly higher than that of undoped ZnO.

Construction of direct Z-scheme g-C3N4/BiYWO6 heterojunction photocatalyst with enhanced visible light activity towards the degradation of methylene blue.

Construction of the Z-scheme heterojunction photocatalyst achieved highly improved photocatalytic ability by its high redox ability of the photoinduced e--h+ pairs. In the study, Z-scheme g-C3N4/BiYWO6 heterojunction photocatalyst is prepared by the single-step hydrothermal method. Further, its photocatalytic ability was assessed by degrading methylene blue under visible light exposure. Particularly, the optimized 30 wt% of g-C3N4 in the g-C3N4/BiYWO6 composite exposes almost complete degradation after 90min, that is ~ 3.0 times greater than the bare BiYWO6 and g-C3N4 with the rate constant value 0.032min-1. Experimentally, the radical trapping studies indicate O2·- and ·OH radicals are playing a vital role in the photocatalytic degradation process. Also, the Z-scheme g-C3N4/BiYWO6 heterojunction photocatalyst exhibits excellent photoelectrochemical property and it is stable after 5 cycles, which indicates its good reusability nature. These enhancements are due to the newly formed heterostructure that facilitates the migration and separation efficiency of the photoproduced e--h+ pairs. Hence, the synthesized Z-scheme g-C3N4/BiYWO6 heterostructure could be an excellent material for wastewater remediation works.

Pyropheophorbide-a/(001) TiO2 Nanocomposites with Enhanced Charge Separation and O2 Adsorption for High-Efficiency Visible-Light Degradation of Ametryn.

It is highly desired to enhance charge separation and O2 adsorption of the pyropheophorbide-a (Ppa) to promote visible-light activity and stability. Herein, Ppa modified 001-facet-exposed TiO2 nanosheets (Ppa/001T) nanocomposites with different weight ratios were fabricated via the self-assembly approach by OH induced. Compared with the bare Ppa, the 8% amount optimized 8Ppa/001T sample displayed 41-fold enhanced activity for degradation of Ametryn (AME) under visible-light irradiation. The promoted photoactivities could be attributed to the accelerated charge carrier’s separation by coupling TiO2 as thermodynamic platform for accepting the photoelectrons with high energy from Ppa and the promoted O2 adsorption because of the residual fluoride on TiO2. As for this, a distinctive two radicals (•O2− and •OH) involved pathway of AME degradation is carried out, which is different from the radical pathway dominated by •O2− for the bare Ppa. This work is of utmost importance since it gives us detailed information regarding the charge carrier’s separation and the impact of the radical pathway that will pave a new approach toward the design of high activity visible-light driven photocatalysts.

Enhanced visible-light activation of persulfate by g-C3N4 decorated graphene aerogel for methyl orange degradation

In the present work, the degradation of methyl orange (MO) by visible-light-driven photocatalytic activation of persulfate (PDS) was studied. Macro-aerogel g-C3N4-doped graphene aerogel (GA) composite with stratified structure was fabricated by a simple hydrothermal method and applied as a recoverable heterogeneous catalyst along with visible light (VL) irradiation for activation of PDS. The microstructure, physical-chemical and photoelectrochemical properties of composite catalysts were characterized and various reaction parameters including the reaction systems, catalyst activator dose, PDS concentration, g-C3N4 doping amount and the initial pH of the solution were evaluated on the MO removal efficiency. Photocatalytic activation of GA for MO degradation was enhanced significantly after modified by g-C3N4. Under optimum conditions (15 mg/L MO, 75 mg/L PDS and 0.012 g/L GCN-3), the catalytic efficiency of g-C3N4 doped GA with the mass ratio of 3:7 (GCN-3) was 2.96 times than that of GA. The strengthening effect of GCN-3 benefited from the synergistic effect of the photogenerated hole (h+), the CO functional groups and rapid electron transfer in GCN-3/VL/PDS system. Given the flexibility and recyclability of GCN-3, the GCN-3/VL/PDS system is a promising technique for practical wastewater purification.

Synergistic effect of novel Co-modified micro/nano geopolymers in a photo-PDS system

Persulfate activation is an efficient advanced oxidation process for water treatment. However, many catalyst materials make their preparation methods and raw materials very complicated and expensive while pursuing high-efficiency catalytic effects. In this research, a novel Co-modified micro/nano geopolymer (Co-MNG) material was prepared from solid waste using a mechanochemical method. The whole preparation process of Co-MNG is simple and time-saving, and most of its raw materials are solid waste. In addition, it has few adverse effects on the environment during preparation and use and has a good effect on PDS activation. Under dark conditions, 1 mg L−1 of unloaded Co metal MNG material could degrade 20 mg L−1 Rhodamine B solution by 79% in 60 min with 15 mM PDS, but the application of visible light could not enhance its effect. However, after adding 4 wt% of different Co-containing compounds, the prepared Co-MNG materials could improve their degradation effect under the same conditions, and it is more obvious under the condition of applying visible light. Among them, MNG-Co(NO3)2 could completely degrade RhB within 40 min under the application of visible light. ESR (electron spin resonance) tests showed that the MNG-Co(NO3)2 material could generate a variety of active radicals in a photo-PDS system, such as h+, ·OH, ·O2− and SO4−. Mechanistic research experiments showed that both visible light and Co-MNG materials can activate PDS to a certain extent, but when both exist at the same time, the material could effectively couple visible light and Co activation of PDS in a photo-PDS activation system to achieve synergistic degradation of pollutants in water.

Controlled preparation of Bi/BiOCl with enhanced catalytic activity for organic pollutant under visible light using one-pot hydrothermal technology

Flowerlike Bi/BiOCl was prepared by one-pot hydrothermal method, where Bi(NO3)3 was used as Bi source, NiCl2 was used as employed as Cl source and co-catalyst, DMF was adopted as cosolvent and reducing agent. In the presence of NiCl2, the reduction of Bi(NO3)3 was accelerated. The prepared conditions were optimized. The prepared Bi/BiOCl showed high photocatalytic activity for rhodamine B (RhB) degradation within 200 s under visible light irradiation. The degradation efficiency and degradation reaction rate for Bi/BiOCl were 98.7% and 1.194 min −1, which was significantly better than that of BiOCl (6.6% and 0.0240 min −1). The improvement of photocatalytic activity was attributed to the successful in-situ formation of Bi metal in the sample, which greatly improved the visible light activity of BiOCl, increased the transfer rate of the photogenerated electron, and inhibited the recombination of photogenerated electron-hole pairs. The prepared Bi/BiOCl presented high cyclic stability and low Bi element leakage of 1.2 ng L−1. The conversion of N element in RhB was preliminarily studied, and the results showed that N element was effectively converted into ammonium. Moreover, the decreased toxicity after RhB degradation was investigated and confirmed by mung bean cultivation with RhB solution before and after degradation.

Visible light responsive Cu-N/TiO2 nanoparticles for the photocatalytic degradation of bisphenol A.

Visible light active co-doped Cu-N/TiO2 photocatalyst was synthesized by the sol-gel method. The synthesized catalysts were characterized by X-ray diffraction (XRD), field-emission transmission electron microscope (FE-TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and UV-visible diffuse reflectance spectrophotometry (UV-vis DRS). The co-doping with Cu-N reduced the bandgap (∼2.83 eV) and extended the optical absorption range of TiO2 catalysts to the visible region. The incorporation of Cu and N on TiO2 lattice results in sub-conduction and valence band formation, which enhanced the photoactivity and electron-hole generation rate. The visible light activity of Cu-N/TiO2 was evaluated via photocatalytic degradation of bisphenol A (BPA) under blue LED illumination. The maximum BPA degradation of 42.7% was observed at 0.5 g L-1 catalyst dosage, initial pH of BPA solution = 8.2, and initial BPA concentration of 10 ppm. Further, a possible mechanism of photocatalytic degradation of BPA was also established.

Facile modification of TiO2 nanoparticles with H2O2 + NH4F for enhanced visible light photodegradation of rhodamine B and methylene blue

We report a facile modification method to increase the visible light activity of TiO2 samples. We use titanium isopropoxide (TTIP) as the raw Ti source, hydrolyzing in acidic and alkaline solutions, respectively, to fabricate different TiO2 samples as raw TiO2 together with P25-TiO2. Only hydrogen peroxide and ammonia fluoride are used for this facile modification method, and three TiO2 samples are modified for the visible light degradation. This method could promote the transformation of crystalline TiO2 from rutile to anatase, increase the specific surface area, and the bandgap of samples shift to lower energy (2.2 – 3.0 eV) after the modification. For the visible light photodegradation tests, all the three modified samples show a higher visible light photodegradation efficiency. The highest kinetic constant of Rhodamine B and methylene blue degradation is 7 and 2 times that of P25, respectively. Additionally, TiO2 fabricated by TTIP in alkaline solution and its as-modified sample show the highest adsorption of methylene blue dye, whose adsorption rate reaches 9 times that of P25. Thus, the present facile modification can effectively improve the photocatalytic ability of TiO2 under visible light.