Photocatalytic degradation of organic pollutants and inactivation of pathogens under visible light via CoOx surface-modified Rh/Sb-doped SrTiO3 nanocube

Visible light-active rhodium and antimony-co-doped SrTiO₃ nanocubes (Rh/Sb:SrTiO₃ NCs) were synthesized at low temperatures from Rh/Sb:TiO₂ nanorods by the molten salt flux method. The effects of different calcination temperatures (700, 800, and 900 °C) and addition of transition metal oxides (NiO_x, CoO_x, and CuO_x) on the photocatalytic properties of the Rh/Sb:SrTiO₃ NCs were studied. The phase composition and morphology of the Rh/Sb:SrTiO₃ NC photocatalysts (after calcination) were characterized using standard analytical techniques. The synergistic effect of the metal oxides and Rh/Sb:SrTiO₃ NCs boosted the photocatalytic degradation of orange II dye and bisphenol A as well as the inactivation of bacteria. 2 wt% CoO_x-loaded Rh/Sb:SrTiO₃ photocatalyst showed higher photocatalytic performance for the degradation of orange II (96.3%) and bisphenol A (87%) in aqueous solution than Ni (2 wt%) and Cu (2 wt%)-loaded Rh/Sb:SrTiO₃ NC composites. In addition, inactivation of Escherichia coli (96%) and Staphylococcus aureus (97.1%) was achieved over CoO_x (2 wt%)-loaded Rh/Sb:SrTiO₃ for 2 h under visible light irradiation (λ?≥?420 nm). Further, scavenging experiments confirmed that superoxide anion radicals (^·O₂^?) and holes (h⁺) are the major active species and OH^· is a minor species responsible for the photocatalytic degradation of the studied organic pollutants. The synthetic strategy presented here offers a novel approach to the design of highly active visible light active photocatalysts for the removal of organic pollutants and inactivation of bacteria in wastewater.

Graphical abstract

     

Luminescence properties of monodispersed spherical BaWO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> microphosphors for white light-emitting diodes

Monodispersed spheres (1–4 μm in diameter) of BaWO₄:Eu³⁺ (hereafter BWO:Eu) red-phosphor exhibiting intense emission at 615 nm were synthesized via a mild hydrothermal method. X-ray diffraction, scanning electron microscope, photoluminescence excitation and emission spectra, and decay curve were used to characterize the properties of BWO:Eu phosphors. An intense red emission was obtained by exciting either into the ⁵L₆ state with 394 nm or the ⁵D₂ state with 465 nm, that correspond to two popular emission lines from near-UV and blue LED chips, respectively. The values of Ω _2,4 experimental intensity parameters (13.8 × 10⁻²⁰ and 8.2 × 10⁻²⁰ cm²) are determined. The high-emission quantum efficiency of the BWO:Eu phosphor suggests this material could be promising red phosphors for generating white light in phosphor-converted white light-emitting diodes.     

Preparation of visible light responsive g-C3N4/H-TiO2 Z-scheme heterojunction with enhanced photocatalytic activity for RhB degradation

The development of high-efficiency heterojunction with improved photocatalytic property is regarded as a promising way to decontaminate wastewater. In this study, Z-Scheme g-C₃N₄/H-TiO₂ heterojunctions with different proportions were synthesized. The photocatalytic degradation of rhodamine B (RhB) was studied under visible light irradiation. Among them, 10% g-C₃N₄/H-TiO₂ photocatalyst had the best performance, and the degradation rate of RhB was 65% within 120 min. In addition, 10% g-C₃N₄/H-TiO₂ photocatalyst had high stability, and its photocatalytic activity did not decrease significantly after four cycles. Through photocurrent analysis, it is found that the photogenerated carriers have obviously excellent separation and transfer characteristics, which makes the 10% g-C₃N₄/H-TiO₂ photocatalyst have good degradation performance. Electron paramagnetic resonance (ESR) experiments showed that ·OH and ·O₂^? were active radicals during degradation.

     

Synthesis of BiOCl/ZnMoO4 heterojunction with oxygen vacancy for enhanced photocatalytic activity

In this study, a novel oxygen vacancy-rich BiOCl/ZnMoO₄ composites were successfully prepared by a simple two-step method. Experimental results indicated that the content of BiOCl with oxygen vacancies played an important role in photocatalytic performance of OBZM heterostructures. OBZM-5 exhibited a highly enhanced photocatalytic activity under visible light irradiation compared to pure BiOCl, Ov-BiOCl, ZnMoO₄ and other OBZM composites, which can be attributed to the efficient separation and transfer of photogenerated charge carrier. The photocatalytic degradation efficiency of rhodamine B (RhB) can reach 99% within 40 min and almost all of norfloxacin (NOR) can be degradated after 100 min by OBZM-5. In addition, OBZM-5 displayed a good stability during the photocatalytic process, which favored a long-term use. Moreover, a possible photocatalytic mechanism was proposed based on the active species trapping experiments and electron spin resonance (ESR) tests, verifying that the photogenerated holes (h⁺) and ·O₂^? radicals were the dominating active species.

     

Samarium-decorated ZrO2@SnO2 nanostructures,their electrical,optical and enhanced photoluminescence properties

In the present work, pure ZrO₂@SnO₂ and Samarium (Sm_x) (x?=?1%, 8% and 12%)-doped ZrO₂@SnO₂ nanoparticles (NPs) successfully synthesized by facile low-cost co-precipitation technique. As-synthesized nanostructures (NS) were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV–visible, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), Brunauer–Emmett–Teller (BET) spectroscopic investigation. The tetragonal crystal phase of the as-synthesized Sm_x:ZrO₂@SnO₂ NS confirmed by XRD analysis. The observed peak shift in the XRD patterns confirmed incorporation of dopant into host lattice. The Sm_x:ZrO₂@SnO₂ NS present irregular spherical morphology and high agglomeration confirmed by FESEM microscope analysis. The presence of functional groups, chemical bonding, chemical constituents and valence state of the NS confirmed by FT-IR and XPS analysis. The Sm_x:ZrO₂@SnO₂ NS showed higher surface area and smaller optical band gap (454 cm²/g and 2.12 eV) than the pure ZrO₂@SnO₂ NS (189–196 cm²/g and 2.84 eV). Photoluminescence (PL) spectra of undoped ZrO₂@SnO₂ and Sm_x:ZrO₂@SnO₂ NS exhibited oxygen vacancies. Undoped ZrO₂@SnO₂ NS exhibited emission intensity at 370.6 nm (λ_excitation?=?300 nm) whereas, Sm_x:ZrO₂@SnO₂ NS showed emission intensities at 453.4 nm, 476.3 nm, 601.3 nm (λ_excitation?=?300 nm). Electrical property studies of Sm_x:ZrO₂:SnO₂ (1%, 8% and 12%) NS showed large variation in Hall constant (0.125?×?10⁶ cm²/coulomb to 0.647?×?10⁶ cm²/coulomb) with proportionately large variation in the resistivity (147.8 Ω-cm to 456.8 Ω-cm) for all the doped samples as compared with pure ZrO₂@SnO₂ NS. The Sm³⁺-doped ZrO₂@SnO₂ NS showed higher stability, intense PL emission and enhanced electrical properties.

     

Facile synthesis of Ti3C2 MXene-modified Bi2.15WO6 nanosheets with enhanced reactivity for photocatalytic reduction of Cr(VI)

Through a facile hydrothermal method, we have successfully prepared Ti₃C₂/Bi_2.15WO₆ (TC/BWO) composite, and systematically investigated their reactivity for the photocatalytic reduction of Cr(VI) under visible light. X-ray diffraction and Raman analysis confirm the formation of heterostructure between Bi_2.15WO₆ and Ti₃C₂. The resultant 7TC/BWO composite exhibits enhanced photoactivity toward Cr(VI) reduction. After 120 min irradiation, the conversion of Cr(VI) reaches 92.5% with the quasi-first-order kinetic constant of k = 0.0145 min^?1, which is higher than that of pure BWO (30% and k = 0.0005 min^?1). The electrochemical and photoluminescent characterization confirm that the introduction of Ti₃C₂ is conducive to the separation of carriers, thus significantly improves the photocatalytic performance of TC/BWO. Furthermore, the radical capture experiments verify that the electrons are important for enhancing reduction of Cr(VI) to Cr(III). As a result, this research provides a comprehensive understanding of the reduction of Cr(VI) by TC/BWO composite under visible light.     

Visible light induced photocatalytic performance of Mn-SnO2@ZnO nanocomposite for high efficient cationic dye degradation

In this work, we have synthesized Mn-doped SnO₂@ZnO nanocomposite for photo degradation of Methylene blue and Rhodamine B dyes upon visible light irradiation. The crystal structure, functional group, optical absorption, defect related emission, morphology, purity and binding energy state of synthesized samples were identified by using various analytical tools. The crystal structure revealed the rutile tetragonal, hexagonal wurtzite for SnO₂ and ZnO samples and the average crystal sizes were found in the range of 23.3 nm to 16.7 nm for the synthesized samples. The optical absorption peaks were shifted to higher wavelength side and optical band gap values were found between 3.52 eV and 2.77 eV which confirm the formation of hetero-junction of SnO₂@ZnO composites. The field emission scanning electron spectroscopy (FESEM) revealed the spherical grain morphology for pure and composite samples. The energy dispersive spectra (EDS) and element mapping confirms the purity of the synthesized samples. The X-ray photoelectron spectroscopy (XPS) revealed that the composition and energy state of Mn⁴⁺, Sn⁴⁺ and Zn²⁺ for composite samples. The photocatalytic degradation results clearly indicate that the Mn-doped SnO₂@ZnO nanocomposite has higher degradation efficiency of 98% and 92% for the Methylene blue and Rhodamine B dyes, respectively and is higher than the other synthesized samples. The present study reveals a low cost and highly efficient photo-catalyst which works up on visible light irradiation for the purification of waste water from industries.

     

Investigation on photogenerated radicals of some carboxylates in solution and in aqueous dispersions of AgBr

Abstract

The photogenerated free radicals from formate, oxalate and acetate in aqueous solutions without and with dispered AgBr grains under illuminations of 355 nm laser light, natural light and monochromatic red, green or blue light were detected by electron spin resonance with spin-trap DMPO. The results showed that: (a) ·CO₂^? radicals were produced in the formate solution by all of these illuminations; (b) the signals of ·CO₂^? radicals were greatly intensified when an AgBr dispersion was present in the formate solution; (c) the signals of ·CO₂^? radicals in the oxalate solution were also detected and intensified when an AgBr dispersion was present, but only after illumination by the 355 nm laser; (d) ·CH₃ radicals, instead of ·CO₂^?, were weakly detected in the acetate solution, but only in the presence of AgBr under illumination by the 355 nm laser. The photochemical behaviour of these carboxylates, particularly formate and oxalate, perhaps implies their capability for trapping photogenerated holes and their potential for acting as a hole converter to an effective electron carrier.     

Efficient decolorization of azo dye Reactive Black B involving aromatic fragment degradation in buffered Co/PMS oxidative processes with a ppb level dosage of Co-catalyst

In order to generate powerful radicals as oxidizing species for the complete decolorization and degradation of azo dye Reactive Black B (RBB) at near neutral pH (pH 6), homogeneous activation of peroxymonosulfate (Oxone: PMS) by the trace Co²⁺-catalysts was explored. We not only took advantage of the high oxidation–reduction potential of produced hydroxyl and sulfite radicals but also an opportunity to oxidize RBB to less complex compounds with extremely low dosages, especially the ppb level of the Co²⁺-catalyst (stoichiometric ratio: [Co²⁺]₀/[RBB]₀ = 1.7 × 10⁻⁶–1.7 × 10⁻⁵; [PMS]₀/[RBB]₀ = 8–32). Anion effects and pH effects were also carried out and discussed to simulate an actual application such as that of a textile waste stream. Both the degradations of RBB and its derivative aromatic fragments were illustrated successfully at UV–visable absorptions of 591 and 310 nm, respectively, and the possible relationships between them were also proposed and discussed, based on the experimental results. The RBB degradation in this Co²⁺/PMS oxidative process successfully formulated a pseudo-first-order kinetic model at an isothermal condition of 25 °C with or without different anions present. The initial rate and rate constant were calculated under different comparative conditions, and the results indicate that the activity of both RBB decolorization and its degradation are not obviously dependent on the PMS concentration, but rather are related to the Co²⁺ dosage.     

The fast degradation for tetracycline over the Ag/AgBr/BiOBr photocatalyst under visible light

A series of Ag/AgBr/BiOBr photocatalysts with different weight contents of Ag/AgBr were successfully constructed via a simple precipitation method in 80 °C water bath. Photocatalysts were characterized by XRD, XPS, SEM, TEM, N₂ Adsorption-Desorption (BET), and UV–Vis Diffuse Reflectance Spectroscopy (DRS). Compared with BiOBr and Ag/AgBr, all the composite photocatalysts show the prominent photocatalytic activity for the degradation of tetracycline (TC). Especially, 1:5Ag/AgBr/BiOBr (20%) has the highest reaction rate constant (kapp?=?0.20 min^?1). Moreover, according to the results of radical scavengers runs, ·OH and h⁺ acted as the main reactive species in the degradation process. Based on above, a possible photocatalytic mechanism for organics degradation over Ag/AgBr/BiOBr was proposed. Interestingly, the redox cycle between O₂/·O₂^? and Br^?/Br⁰ assisted with the surface plasmon resonance (SPR) effect of silver dramatically promotes the separation and transfer of electron–hole pairs, and improves the photocatalytic activity of the as-obtained composite samples.

     

Synthesis of AgBr/TiO2/(I/S) composite and its enhanced photocatalytic performance to rhodamine B

Novel AgBr/TiO₂/(I/S) composite was synthesized by deposition–precipitation method. The AgBr/TiO₂/(I/S) composite was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectra, UV–Vis diffuse reflectance spectra and the N₂ adsorption/desorption instrument. Under visible light irradiation, AgBr/TiO₂/(I/S) composite displayed much higher photocatalytic activity than that of pure I/S in the degradation of Rhodamine B (RhB). The RhB dye was degraded by 89% in less than 100 min. All results indicated that AgBr/TiO₂/(I/S) composite have good photocatalytic activity and chemical stability. Moreover, ·O₂^? is demonstrated to be the dominant radical for the photocatalytic degradation of RhB.

     

Preparation and characterization of Cu-doped TiO2 nanomaterials with anatase/rutile/brookite triphasic structure and their photocatalytic activity

Pure TiO₂ and Cu–doped TiO₂ containing different amounts of copper ions with anatase/rutile/brookite triphasic structure were successfully synthesized through a simple hydrothermal method. The obtained samples were characterized by X–ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), transmission electron microscope (TEM), X–ray photoelectron spectroscopy (XPS), UV?vis diffuse reflectance spectroscopy (UV-DRS), photoluminescence spectroscopy (PL) and Brunauer–Emmett–Teller surface area analyze (BET). Both pure and Cu–doped TiO₂ show relatively high photocatalytic activity owing to their considerable surface areas. Moreover, the three–phase coexisting structure and the conversion between Cu²⁺ and Cu⁺ ions facilitate the separation of photogenerated electrons and holes, which is favorable for photocatalytic performance. 1%Cu–TiO₂ exhibits the highest photocatalytic activity and the degradation degree of rhodamine B (RhB) reaches 93.5% after 30 min, which is higher than that of monophasic/biphasic 1%Cu–TiO₂. ·O₂^? radical is the main active species, and h⁺ and ·OH species are subsidiary in the degradation process.

     

The Ag-based SPR effect drives effective degradation of organic pollutants by BiOCOOH/AgBr composites

The easy recombination of electron-hole pairs produced by monomeric photocatalysts under light exposure severely limits their application in wastewater treatment. Based on this, BiOCOOH/Ag/AgBr ternary photocatalysts in flower-like microspheres were controllably synthesized by precipitation photoreduction and characterized by various techniques. In addition, the effects of different molar ratio of BiOCOOH and AgBr, catalyst dose, pH and coexisting ions on the photocatalytic degradation of rhodamine B (RhB) and tetracycline (TC) were investigated. The results showed that the BOC/Ag/AgBr-0.5 composite exhibited excellent photocatalytic activity for the degradation of RhB and TC. The excellent photocatalytic activity was mainly attributed to the surface plasmon resonance (SPR) effect of metallic Ag and charge transfer mechanism between composites, thus promoting charge separation. The degradation efficiency of RhB and TC was 92.7% and 72.3% with the degradation rate constant of 0.073 and 0.023 under light irradiation of xenon lamp in 30 and 45 min, respectively, which was 6 and 2 times higher than that of BiOCOOH and AgBr. The stability studies showed that BOC/Ag/AgBr-0.5 maintained a high catalytic activity after four cycles. The results of radical capture experiments showed that h⁺ and ·O₂^– were the main reactive radicals, while ·OH played a secondary role in the photocatalytic system. Subsequently, a potential photocatalytic mechanism was proposed based on the experimental results.     

The effect of GdF3 on red emission of Eu3+: LiYF4 single crystals grown by the Bridgman method

The bulk LiYF₄ single crystals with high-quality doped 0.5 mol% Eu³⁺ and various Gd³⁺ from 1.5 to 4.5 mol% in size of about Φ 10?×?65 mm were successfully grown by an improved Bridgman method. The X-ray diffraction (XRD) measurement and Rietveld refinement analysis were conducted to verify the structure of the obtained crystal crystals. The spectroscopic properties of the single crystals as change of GdF₃ concentration were investigated with the help of absorption, excitation, emission spectra, and decay curves of their fluorescence. The characteristic absorption bands of Gd³⁺ at 277 nm and Eu³⁺ at 395 nm were observed in the co-doped samples. Significant enhanced emission intensity of 613 nm was observed as increasing of GdF₃ content into Eu³⁺:LiYF₄ single crystal upon excitations of both 277 nm and 395 nm lights. The former was owing to the energy transfer (ET) between Gd³⁺ and Eu³⁺, while the latter was due to the change of crystal field environment around Eu³⁺ by the increasing of GdF₃ content. The ET from Gd³⁺ to Eu³⁺ ions was further confirmed from the result of the luminescence decay analysis. Besides, the full width half-maximum (FWHM) of 613 nm emission band was estimated to be?~?4.5 nm. The Eu³⁺/Gd³⁺ co-doped LiYF₄ single crystal with excellent optical and physicochemical properties might has significant applications in red laser and display devices.

     

Bi2WO6/NH2-MIL-88B(Fe) heterostructure: An efficient sunlight driven photocatalyst for the degradation of antibiotic tetracycline in aqueous medium

The development of highly efficient sunlight assisted photocatalysts has been acknowledged as a promising strategy for the enhanced degradation of antibiotics. In this work, effectual fabrication of a novel Bi₂WO₆/NH₂-MIL-88B(Fe) heterostructure was carried through solvothermal route. The structural, morphological and compositional analysis was done by employing number of analytical techniques, namely XRD, FTIR, HRTEM, FESEM, XPS, PL and BET surface area. The prepared Bi₂WO₆/NH₂-MIL-88B(Fe) heterostructure was utilized as an efficient photocatalyst towards decomposition of a typical antibiotic tetracycline (TC) in aqueous medium. It was found that Bi₂WO₆/NH₂-MIL-88B(Fe) heterostructure exhibited improved degradation efficiency of about 89.4% within 130 min of solar illumination than pristine NH₂-MIL-88B(Fe) under optimized parameters i.e. initial drug solution of 10 mg/L concentration at pH 4 with 0.35 g/L dose of catalyst. Moreover, adsorption studies, kinetics and isotherms of adsorption on TC were also investigated. Results revealed that adsorption kinetics followed pseudo 2nd order model and isotherm data fitted well with Freundlich model (R² = 0.99803) as compared to Temkin and Langmuir. The ameliorating photocatalytic capability could be primarily accredited to the heterojunction created among Bi₂WO₆ and NH₂-MIL-88B(Fe) which facilitated the charge transfer and thus determines high catalytic efficiency. The enhanced photocatalyic effect was further verified by electrochemical impedance and photocurrent studies. The prepared composite also exhibited longer carrier lifetime (140.72 ns) compared to pure MOF (132.05 ns) and Bi₂WO₆ (136.39 ns). Further, based on the radical trapping investigations, role of superoxide radicals was dominant and detailed mechanism was proposed for the photocatalytic degradation process. The major intermediates formed during the course of reaction were also examined using LCMS analysis. The photodegradation was also carried over simulated hospital wastewater by the prepared heterostructure and 60.5% TOC was obtained under solar light in 390 min. Moreover, the synthesized heterostructure showed good recyclability up to three cycles depicting good stability.     

Skillfully grafted CO functional group to enhance the adsorption/photocatalytic mechanism of YMnO3/MgAl2O4 heterojunction photocatalysts

The YMnO₃ with different manganese salts includes MnSO₄·H₂O, MnCO₃ and C₄H₆MnO₄·4H₂O and YMnO₃/MgAl₂O₄ heterojunction photocatalysts (YMO/MAO) with different mass percentage of MgAl₂O₄ were synthesized by a simple wet chemistry method combined with low temperature sintering technology. The effects of manganese salts on the structure, functional groups, morphology, charge states and optical properties of YMnO₃ phase were studied in detail. The pure YMnO₃ with the uniformity of particles can be obtained when only C₄H₆MnO₄·4H₂O is used as manganese source. The results confirmed that the YMO/MAO heterojunction was constructed by one step low-temperature sintering technique. The YMnO₃/wt 10 % MgAl₂O₄ photocatalyst exhibits high optical absorption coefficient and highest adsorption capacity of 122.86 mg/g and degradation percentage of 98.98 % for the degradation of Congo red (CR), 86.16 % for the degradation of tetracycline hydrochloride (TC) and 72.51 % for the degradation of tetrabromo bisphenol A (TBBPA). The hydroxyl and superoxide radicals dominated the photocatalytic reaction process of YMO/MAO for the degradation of CR, TC and TBBPA. The present work pioneers the potential application of YMO/MAO grafted by CO functional group as dyes, antibiotics and persistent organic pollutants (POPS) adsorption / degradation catalyst and further provides technical reference for the synthesis of others heterojunction photocatalysts.     

Controllable Exfoliation of MOF-Derived Van Der Waals Superstructure into Ultrathin 2D B/N Co-Doped Porous Carbon Nanosheets: A Superior Catalyst for Ambient Ammonia Electrosynthesis

The electrocatalytic nitrogen reduction reaction (NRR) to synthesize NH₃ under ambient conditions is a promising alternative route to the conventional Haber–Bosch process, but it is still a great challenge to develop electrocatalysts’ high Faraday efficiency and ammonia yield. Herein, a facile and efficient exfoliation strategy to synthesize ultrathin 2D boron and nitrogen co-doped porous carbon nanosheets (B/N C NS) via a metal–organic framework (MOF)-derived van der Waals superstructure, is reported. The results of experiments and theoretical calculations show that the doping of boron and nitrogen can modulate the electronic structure of the adjacent carbon atoms; which thus, promotes the competitive adsorption of nitrogen and reduces the energy required for ammonia synthesis. The B/N C NS exhibits excellent catalytic performance and stability in electrocatalytic NRR, with a yield rate of 153.4 µg·h⁻¹·mg⁻¹ cat and a Faraday efficiency of 33.1%, which is better than most of the reported NRR electrocatalysts. The ammonia yield of B/N C NS can maintain 92.7% of the initial NRR activity after 48 h stability test. The authors’ controllable exfoliation strategy using MOF-derived van der Waals superstructure can provide a new insight for the synthesis of other 2D materials.     

Growth mechanism and photocatalytic properties of SrWO4 microcrystals synthesized by injection of ions into a hot aqueous solution

This paper reports our initial research to obtain SrWO₄ microcrystals by the injection of ions into a hot aqueous solution and their photocatalytic (PC) properties. These microcrystals were structurally characterized by X-ray diffraction (XRD), Rietveld refinements and Fourier transform (FT)-Raman spectroscopy. The shape and average size of these SrWO₄ microcrystals were observed by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). In addition, we have investigated the PC activity of microcrystals for the degradation of rhodamine B (RhB) and rhodamine 6G (Rh6G) dyes. XRD patterns, Rietveld refinement data and FT-Raman spectroscopy confirmed that SrWO₄ microcrystals have a scheelite-type tetragonal structure without deleterious phases. FT-Raman spectra exhibited 12 Raman-active modes in a range from 50 to 1000 cm^?1. FE-SEM and TEM images suggested that the SrWO₄ microcrystals (rice-like – 95%; star-, flower-, and urchin-like – 5%) were formed by means of primary/secondary nucleation events and self-assembly processes. Based on these FE-SEM/TEM images, a crystal growth mechanism was proposed and discussed in details in this work. Finally, a good PC activity was first discovered of the SrWO₄ microcrystals for the degradation of RhB after 80 min and Rh6G after 50 min dyes under ultraviolet-light, respectively.     

Application of response surface methodology to optimize high active Cu-Zn-Al mixed metal oxide fabricated via microwave-assisted solution combustion method

The present work deals with evaluation of decisive parameters on performance and structure of Cu_0.4Zn_0.6Al₂O₄ catalyst. In this respect, the experiments were designed by the response surface methodology (RSM), considering the main parameters: the amounts of urea and ammonium acetate and the activity were assessed in esterification reaction. The results of statistical analysis showed that the proposed second-order equation is highly compatible with experimental data and the interaction between the ratios of both fuel types is highly effective as well independent variables. The catalyst synthesized with the fuel content higher than the stoichiometric ratio (67% urea and 45% ammonium acetate) has the highest catalytic activity in the esterification reaction, where the efficiency of about 98.2% is obtained in the esterification reaction under the conditions of 180 °C, methanol to oleic acid molar ratio of 9, 3 wt% of catalyst and 6 h of reaction time. The sample fabricated with 67% urea and 45% ammonium acetate as fuel (more than stoichiometric ratio) presented the highest activity that could convert 98.2% of oleic acid to ester. Characterization of the catalysts showed that the particle size reduced from about 18 nm for the catalyst synthesized with single fuel to 12 nm for that synthesized at fuel rich condition. Moreover, the unit cell size was meaningfully changed by using combined fuel that can be related to incorporation of simultaneous Zn and Cu for preparation of aluminate structure. As well as use of combination urea and ammonium acetate led to increase the textural properties (surface area from 4.76 m²·g⁻¹ to 8.39 m²·g⁻¹ and mean pore size from 2.1 nm to 8.9 nm). The results can confirm formation of dopant structure of Zn/CuAl₂O₄ in which a few amount of single phase was detected.     

Twisty C-TiO2/PCN S-Scheme Heterojunction with Enhanced n→π * Electronic Excitation for Promoted Piezo-Photocatalytic Effect

Herein, a twisty C-TiO₂/PCN (CNT) Step-scheme (S-scheme) heterojunction is fabricated and applied to degrade ciprofloxacin (CIP) with the assistance of ultrasonic vibration and visible light irradiation. The nitrogen-rich twisty polymeric carbon nitride (PCN) can not only induce a non-centrosymmetric structure with enhanced polarity for a better piezoelectric effect but also provide abundant lone pair electrons to promote n→π* transition during photocatalysis. Its hybridization with C-TiO₂ particles can construct S-scheme heterojunction in CNT. During the piezo-photocatalysis, the strain-induced polarization electric field in the heterojunction can regulate the electron migration between the two components, resulting in a more effective CIP degradation. With the synergistic effect of ultrasonic vibration and visible light irradiation, the reaction rate constant of CIP degradation by CNT increases to 0.0517 min⁻¹, which is 1.86 times that of photocatalysis and 6.46 times that of ultrasound. This system exhibits a stable CIP decomposition efficiency under the interference of various environmental factors. In addition, the in-depth investigation found that three pathways and 12 major intermediates with reduced toxicity are produced after the reaction. Hopefully, the construction of this twisty CNT S-scheme heterojunction with enhanced piezo-photocatalytic effect offers inspiration for the design of environmentally functional materials.