Emerald eco-synthesis: harnessing oleander for green silver nanoparticle production and advancing photocatalytic MB degradation with TiO2&CuO nanocomposite

The tertiary composite of TiO2/CuO @ Ag (TCA) were synthesized by the solid state method using different ratios of TiO2/CuO NCs and Ag NPs. The structural, morphological, and optical properties of nanocomposites were analyzed by scanning electron microscope, Transmission electron microscope, X-ray diffraction, Fourier transform infrared spectra, UV-Vis diffuse reflectance spectra (UV-Vis/DRS) and photoluminescence spectrophotometry. The results showed enhanced activity of TCA hybrid nano crystals in oxidizing MB in water under visible light irradiation compared to pure TiO2. The photocatalytic performance TCA samples increased with suitable Ag content. The results show that the photo degradation efficiency of the TiO2 compound improved from 13 to 85% in the presence of TiO2-CuO and to 98.87% in the presence of Ag containing TiO2-CuO, which is 7.6 times higher than that of TiO2. Optical characterization results show enhanced nanocomposite absorption in the visible region with long lifetimes between e/h+ at optimal TiO2-CuO/Ag (TCA2) ratio. Reusable experiments indicated that the prepared TCA NC photo catalysts were stable during MB photo degradation and had practical applications for environmental remediation.

Selective photocatalytic aerobic oxidation of methane into carbon monoxide over Ag/AgCl@SiO2

Design of active catalysts for chemical utilization of methane under mild conditions is of great importance, but remains a challenging task. Here, we prepared a Ag/AgCl with SiO₂ coating (Ag/AgCl@SiO₂) photocatalyst for methane oxidation to carbon monoxide. High carbon monoxide production (2.3 μmol h⁻¹) and high selectivity (73%) were achieved. SiO₂ plays a key role in the superior performance by increasing the lifetime of the photogenerated charge carriers. Based on a set of semi in situ infrared spectroscopy, electron paramagnetic resonance, and electronic property characterization studies, it is revealed that CH₄ is effectively and selectively oxidized to CO by the in situ formation of singlet ¹O₂via the key intermediate of COOH*. Further study showed that the Ag/AgCl@SiO₂ catalyst could also drive valuable conversion using real sunlight under ambient conditions. As far we know, this is the first work on the application of SiO₂ modified Ag/AgCl in the methane oxidation reaction.

The Ag/AgCl@SiO₂ catalyst exhibits excellent photocatalytic activity in selective aerobic oxidation of methane to carbon monoxide with high selectivity, and extended real light simulation feasibility shows potential in practical application.

Silver nanoparticle-decorated TiO2 nanotube array for solid-phase microextraction and SERS detection of antibiotic residue in milk

The excessive use or abuse of antibiotics on dairy cows leads to residues in milk, which can represent a public health risk. However, in recent years the β-Lactamase was illegally used to degrade residual antibiotics in milk, which makes the traditional antibiotic detection methods ineffective. Therefore, there is an extremely urgent need for multi-analyte analysis techniques for the detection of antibiotic residues. Herein, we reported an ultra-fast, facile, and sensitive solid-phase microextraction (SPME)-surface enhanced Raman scattering (SERS) platform for the detection of degraded antibiotics-2-mercapto-5-methyl-1,3,4-thiadiazole (MMT). The results showed that the log-log plot of SERS intensity to MMT concentration exhibits a superior linear relationship (R² = 0.992) in the concentration range of 0.5-1000 μM, with a detection limit of 0.11 μM. The silver nanoparticle-decorated TiO₂ nanotube array was successfully used as an all-in-one SPME-SERS substrate in the extraction and identification of the antibiotic degradation products in real milk. Due to the rapid pre-treatment, good reproducibility, and self-cleaning, the proposed SPME-SERS method has a great promise to be applied as a powerful tool for on-site detection in the field of food safety.

Eco-friendly hybrid Paper-AgBr-TiO2 for efficient photocatalytic aerobic mineralization of ethanol

In this study, a facile and effective route to prepare hybrid photocatalysts (paper-TiO₂, paper-TiO₂-AgBr and paper-AgBr-TiO₂) has been reported. The preparation procedure consisted of the direct adsorption of the previously synthesized titania nanoparticles (TiO₂ sol) to generate the TiO₂ nanosphere and the immersion process in an aqueous suspension of AgBr to form the AgBr nanoclusters on paper fibers. The synthesis technology is economic, efficient, environmentally friendly and easy to implement even at industrial scale. A cellulose-based structure with well dispersed TiO₂ particles of around 1 μm and a pseudo-liquid coating of Ag⁺ and AgBr species was obtained. All the prepared photocatalysts demonstrated effective photocatalytic performance in gaseous phase ethanol degradation with simulated sunlight illumination, through the direct mineralization to CO₂ and the parallel reaction via acetaldehyde degradation. A relevant improvement in the photocatalytic activity was noticed when TiO₂ was associated with AgBr nanocrystals, with a higher effect observed when AgBr was loaded onto the paper surface prior to TiO₂. Ag-Ti interaction reduces the pair recombination rate and increases the available charge carriers generating reactive OH- radicals from both Ag-species and TiO₂, and O₂^- radicals from Ag⁺-AgBr species, which would be involved in the ethanol degradation process.

Paper Functionalized with Nanostructured TiO2/AgBr: Photocatalytic Degradation of 2-Propanol under Solar Light Irradiation and Antibacterial Activity

A facile method to produce paper–TiO₂ decorated with AgBr nanoparticles by a mild hydrothermal process at 140 °C was reported. The synthesis method was based on the immersion of the paper in a ready-made suspension of TiO₂/AgBr, comprising TiO₂ sol solution prepared in acidic conditions and AgBr solution (10⁻⁴ M). A paper–TiO₂ sample was prepared and used as reference. The formation of crystalline phases of titanium oxide (TiO₂) and silver bromide (AgBr) was demonstrated by XRD, Raman and EDX analyses. The surface morphology of the TiO₂–AgBr was investigated by Field Effect Scanning Electronic Microscopy (FE–SEM). The photocatalytic performances of the prepared material were evaluated in the degradation of 2-propanol in the gas phase, under simulated sunlight illumination. Its antibacterial properties against Escherichia coli (E. coli) were also assessed. The efficiency of photodegradation and the anti-bacterial properties of paper–TiO₂–AgBr were attributed to an improvement in the absorption of visible light, the increased production of reactive oxygen species (ROS) and the low recombination of photogenerated charge carriers due to the synergistic effect between TiO₂ and AgBr/Ag nanoparticles.

Butterfly cluster like lamellar BiOBr/TiO2 nanocomposite for enhanced sunlight photocatalytic mineralization of aqueous ciprofloxacin

The present study for the first time reports facile in-situ room temperature synthesis of butterfly cluster like lamellar BiOBr deposited over TiO₂ nanoparticles for photocatalytic breakdown of ciprofloxacin (CIP). The butterfly cluster arrangement of BiOBr resulted in an increase in surface area from 124.6 to 160.797 m²·g^-1 and subsequently increased incident light absorption by the composite photocatalyst. The XRD indicated the existence of TiO₂ as spherical ≈10-15 nm diameter particles with [101] preferential growth planes of anatase phase while the lamellar BiOBr showing growth along [110] and [102] preferential planes that were also confirmed by the HR-TEM images. DRS data implicated 2.76 eV as the energy band gap of the synthesized nanocomposite while PL spectroscopic analysis predicted it to be 2.81 eV. XPS measurements examined the chemical oxidation states of the constituents among the nanocomposite samples. The lameller structure of BiOBr in 15%BiOBr/TiO₂ acts as a manifold promoting both visible light (λ > 420 nm) and direct sunlight catalytic degradation of 25 mg·L^-1 aqueous CIP up to 92.5% and 100%, respectively within 150 min. The rate constant values suggested that the visible light photocatalysis of CIP with 15%BiOBr/TiO₂ was 5.2 and 9.4 times faster compared to pristine TiO₂ and BiOBr, respectively. The free radical scavenging study demonstrated that although photogenerated superoxide ions and holes contribute to the overall photocatalytic activity, yet, hydroxyl radicals predominantly control the CIP oxidation. The synthesized nanocomposite was re-used up to five cycles and retained 82.98% efficiency even after 5th use cycle showing a decline of only 12%. The catalyst stability and easy recovery adds to its reusability and value of the photocatalytic process.

3D Edge-Enriched Fe3 C@C Nanocrystals with a Core-Shell Structure Grown on Reduced Graphene Oxide Networks for Efficient Oxygen Reduction Reaction

The design of highly active, stable, and low-cost oxygen reduction reaction (ORR) electrocatalysts to replace platinum-based materials is crucial to the development of renewable energy technologies. Herein, novel 3D edge-enriched Fe₃ C@C nanocrystals with a core-shell structure grown on reduced graphene oxide (rGO) networks (Fe₃ C@C/rGO) are reported as highly efficient and stable electrocatalysts for the ORR. The rGO nanosheets act as a host and provide vital support for local growth of edge-enriched Fe₃ C@C nanocrystals, leading to a large surface area of 263 m²  g^-1 and superstable hybrid structure. The unique structural design of the Fe₃ C@C/rGO hybrid enables fast mass transport and a substantial number of exposed active edge sites for electrocatalytic reaction. The Fe₃ C@C/rGO hybrid exhibits excellent ORR catalytic activity, with a high positive onset potential close to 1.0 V, a Tafel slope of 65 mV dec^-1 , and excellent durability with only about 8 % current density decay at 0.8 V after 20 000 s continuous operation, which is superior to that of commercial Pt/C catalyst in an alkaline electrolyte.

A novel thermal exfoliation strategy for the fabrication of high-quality Ag/TiO2 nanosnowman nanoparticles with enhanced photocatalytic properties

A novel thermal exfoliation strategy has been proposed to synthesize high-quality Ag/TiO₂ head–body nanosnowman nanoparticles (AgTiNPs, with the head and body being single Ag and TiO₂ nanoparticles, respectively).

Rational design of a novel quaternary ZnO@ZnS/Ag@Ag2S nanojunction system for enhanced photocatalytic H2 production

A novel ZnO@ZnS/Ag@Ag₂S quaternary nanojunction photocatalyst has been designed for efficient solar water splitting.

Uniform carbon dots@TiO2 nanotube arrays with full spectrum wavelength light activation for efficient dye degradation and overall water splitting

This work presents a novel approach for preparing photocatalysts based on TiO₂ nanotube arrays (TiO₂ NTAs) anchored with carbon dots (CDs) by a facile two-step method which includes an electrochemical anodization technique followed by electrochemical deposition. The synthesized high quality graphitic carbon dots can act as sensitizers to extend the spectral range of light absorption towards the full solar spectrum. It is confirmed that TiO₂ NTAs anchored with CDs (CDs/TiO₂ NTAs) display greatly improved photocatalytic activity and excellent photocatalytic stability. By tuning the light absorption of the TiO₂ NTAs, the utilization of light in charge generation and separation is well synergized with the CDs for enhanced photocatalytic pollutant degradation and water splitting, achieving significantly improved rates of photocatalytic degradation and H₂ production in the visible and full spectra, respectively.

Influence of acidic pH on the formulation of TiO2 nanocrystalline powders with enhanced photoluminescence property

Titanium dioxide (TiO2) nanoparticles were prepared by the sol-gel method at different pH values (3.2-6.8) with a hydrochloric acid (HCl) solution. Raw samples were calcined at 500 °C for 2 h. The effects of pH on the structural, morphological and optical properties of TiO2 nanoparticles were investigated. At pH 4.4-6.8, only the anatase phase of TiO2 was observed. Under strong acidic condition at pH 3.2 rutile, brookite and anatase co-exist, but rutile is the predominant phase. The strain value increased and the crystallite size decreased as the HCl content increased. The increased crystallite sizes in the range 21-24 nm and enhanced blue emission intensity around 432 nm was obtained for the sample at pH 5.0. Experimental results showed that TiO2 nanoparticles synthesized at pH 5.0 exhibited the best luminescence property with pure anatase phase.

Hexagonal AgBr crystal plates for efficient photocatalysis through two methods of degradation: methyl orange oxidation and CrVI reduction

Well-defined AgBr-hexagonal crystal plates have been synthesized, which manifested high photocatalytic properties in both the photo-reduction of Cr^VI and the photo-oxidation of methyl orange (MO).

Charge Transport in Two-Photon Semiconducting Structures for Solar Fuels

Semiconducting heterostructures are emerging as promising light absorbers and offer effective electron-hole separation to drive solar chemistry. This technology relies on semiconductor composites or photoelectrodes that work in the presence of a redox mediator and that create cascade junctions to promote surface catalytic reactions. Rational tuning of their structures and compositions is crucial to fully exploit their functionality. In this review, we describe the possibilities of applying the two-photon concept to the field of solar fuels. A wide range of strategies including the indirect combination of two semiconductors by a redox couple, direct coupling of two semiconductors, multicomponent structures with a conductive mediator, related photoelectrodes, as well as two-photon cells are discussed for light energy harvesting and charge transport. Examples of charge extraction models from the literature are summarized to understand the mechanism of interfacial carrier dynamics and to rationalize experimental observations. We focus on a working principle of the constituent components and linking the photosynthetic activity with the proposed models. This work gives a new perspective on artificial photosynthesis by taking simultaneous advantages of photon absorption and charge transfer, outlining an encouraging roadmap towards solar fuels.

Self-assembly graphitic carbon nitride quantum dots anchored on TiO2 nanotube arrays: An efficient heterojunction for pollutants degradation under solar light

In this study, an efficient heterojunction was constructed by anchoring graphitic carbon nitride quantum dots onto TiO2 nanotube arrays through hydrothermal reaction strategy. The prepared graphitic carbon nitride quantum dots, which were prepared by solid-thermal reaction and sequential dialysis process, act as a sensitizer to enhance light absorption. Furthermore, it was demonstrated that the charge transfer and separation in the formed heterojunction were significantly improved compared with pristine TiO2. The prepared heterojunction was used as a photoanode, exhibiting much improved photoelectrochemical capability and excellent photo-stability under solar light illumination. The photoelectrocatalytic activities of prepared heterojunction were demonstrated by degradation of RhB and phenol in aqueous solution. The kinetic constants of RhB and phenol degradation using prepared photoelectrode are 2.4 times and 4.9 times higher than those of pristine TiO2, respectively. Moreover, hydroxyl radicals are demonstrated to be dominant active radicals during the pollutants degradation.

Rough gold films as broadband absorbers for plasmonic enhancement of TiO2 photocurrent over 400-800 nm

Recent years have witnessed an increasing interest in highly-efficient absorbers of visible light for the conversion of solar energy into electrochemical energy. This study presents a TiO₂-Au bilayer that consists of a rough Au film under a TiO₂ film, which aims to enhance the photocurrent of TiO₂ over the whole visible region and may be the first attempt to use rough Au films to sensitize TiO₂. Experiments show that the bilayer structure gives the optimal optical and photoelectrochemical performance when the TiO₂ layer is 30 nm thick and the Au film is 100 nm, measuring the absorption 80–90% over 400–800 nm and the photocurrent intensity of 15 μA·cm⁻², much better than those of the TiO₂-AuNP hybrid (i.e., Au nanoparticle covered by the TiO₂ film) and the bare TiO₂ film. The superior properties of the TiO₂-Au bilayer can be attributed to the rough Au film as the plasmonic visible-light sensitizer and the photoactive TiO₂ film as the electron accepter. As the Au film is fully covered by the TiO₂ film, the TiO₂-Au bilayer avoids the photocorrosion and leakage of Au materials and is expected to be stable for long-term operation, making it an excellent photoelectrode for the conversion of solar energy into electrochemical energy in the applications of water splitting, photocatalysis and photosynthesis.

A bamboo-inspired hierarchical nanoarchitecture of Ag/CuO/TiO(2) nanotube array for highly photocatalytic degradation of 2,4-dinitrophenol

The optimized geometrical configuration of muitiple active materials into hierarchical nanoarchitecture is essential for the creation of photocatalytic degradation system that can mimic natural photosynthesis. A bamboo-like architecture, CuO nanosheets and Ag nanoparticles co-decorated TiO2 nanotube arrays (Ag/CuO/TiO2), was fabricated by using simple solution-immersion and electrodeposition process. Under simulated solar light irradiation, the 2,4-dinitrophenol (2,4-DNP) photocatalytic degradation rate over Ag/CuO/TiO2 was about 2.0, 1.5 and 1.2 times that over TiO2 nanotubes, CuO/TiO2 and Ag/TiO2, respectively. The enhanced photocatalytic activity of ternary Ag/CuO/TiO2 photocatalyst was ascribed to improved light absorption, reduced carrier recombination and more exposed active sites. Moreover, the excellent stability and reliability of the Ag/CuO/TiO2 photocatalyst demonstrated a promising application for organic pollutant removal from water.

Monodisperse Ag–AgBr nanocrystals anchored on one-dimensional TiO2 nanotubes with efficient plasmon-assisted photocatalytic performance

A novel ternary Ag–AgBr/TiO₂ plasmonic nanotube heterojunction photocatalyst was fabricated, showing a very high-performance for decomposition of organic pollutants.

Facile fabrication hybrids of TiO2@ZnO tubes with enhanced photocatalytic properties

Hollow nano-tubes of TiO₂ and TiO₂@ZnO hybrids were produced by a facile and mild approach combining an electrospinning technique and soaking method, followed by calcination.

Highly efficient, stable and controllable multi-core, rattle-type Ag@SiO2 catalyst for the reduction of 4-nitrophenol

Multi-core, rattle-type Ag@silica nanoparticles with different silver loadings were prepared via selective etching methods.

Novel phosphorus doped carbon nitride modified TiO₂ nanotube arrays with improved photoelectrochemical performance

Novel phosphorus-doped graphitic-carbon nitride (P-C3N4) modified vertically aligned TiO2 nanotube arrays (NTs) were designed and synthesized. They can significantly enhance the conduction and utilization of photogenerated charge carriers of TiO2 NTs. The heterostructure was successfully fabricated through a three-step process: electrochemical anodization and wet-dipping followed by thermal polymerization. The prepared P-C3N4/TiO2 NTs exhibit enhanced light-absorption characteristics and improved charge separation and transfer ability, thus resulting in a 3-fold photocurrent (1.98 mA cm(-2) at 0 V vs. Ag/AgCl) compared with that of pure TiO2 NTs (0.66 mA cm(-2) at 0 V vs. Ag/AgCl) in 1 M NaOH solution. The prepared P-C3N4/TiO2 NT photoelectrodes also present excellent photocatalytic and photoelectrocatalytic capabilities in the degradation of methylene blue (MB). The kinetic rate of P-C3N4/TiO2 NTs in the photoelectrocatalytic process for MB is 2.7 times that of pristine TiO2 NTs. Furthermore, the prepared sample was used as a photoanode for solar-driven water splitting, giving a H2 evolution rate of 36.6 μmol h(-1) cm(-2) at 1.0 V vs. RHE under simulated solar light illumination. This novel structure with a rational design for a visible light response shows potential for metal free materials in photoelectrochemical applications.

Advanced nanoarchitectures of silver/silver compound composites for photochemical reactions

Silver/silver compound (SSC) composites have received much attention as a type of potential materials in photochemical reactions due to their high efficiency, facile syntheses and availability of raw materials. This article reviews the state-of-the-art progress on the advanced nanoarchitectures of SSC composites. We begin with a survey on the general synthetic strategies for SSC composites, and then step into relatively detailed methods for size and morphology tunable two-component and more delicate multi-component SSC nanostructures. In addition, the electronic structure-related mechanisms of such materials and the recent studies on their stability are summarized. This review also highlights some perspectives on challenges related to the SSC composites and the possible research in the future.

Synthesis of polypyrrole–titanium dioxide brush-like nanocomposites with enhanced supercapacitive performance

Polypyrrole–titanium dioxide brush-like nanocomposites show enhanced electrochemical performance and excellent cycling stability as an electrode material for supercapacitors.

Recent progress in highly efficient Ag-based visible-light photocatalysts

This review summarizes the recent progress in Ag-compound-based semiconductor photocatalysts, which will provide insights for future photocatalytic designs.

Controlled fabrication of Sn/TiO2 nanorods for photoelectrochemical water splitting

In this work, we investigate the controlled fabrication of Sn-doped TiO2 nanorods (Sn/TiO2 NRs) for photoelectrochemical water splitting. Sn is incorporated into the rutile TiO2 nanorods with Sn/Ti molar ratios ranging from 0% to 3% by a simple solvothermal synthesis method. The obtained Sn/TiO2 NRs are single crystalline with a rutile structure. The concentration of Sn in the final nanorods can be well controlled by adjusting the molar ratio of the precursors. Photoelectrochemical experiments are conducted to explore the photocatalytic activity of Sn/TiO2 NRs with different doping levels. Under the illumination of solar simulator with the light intensity of 100 mW/cm2, our measurements reveal that the photocurrent increases with increasing doping level and reaches the maximum value of 1.01 mA/cm2 at -0.4 V versus Ag/AgCl, which corresponds to up to about 50% enhancement compared with the pristine TiO2 NRs. The Mott-Schottky plots indicate that incorporation of Sn into TiO2 nanorod can significantly increase the charge carrier density, leading to enhanced conductivity of the nanorod. Furthermore, we demonstrate that Sn/TiO2 NRs can be a promising candidate for photoanode in photoelectrochemical water splitting because of their excellent chemical stability.

Highly efficient and stable Ag-AgBr/TiO2 composites for destruction of Escherichia coli under visible light irradiation

A series of Ag-AgBr/TiO2 composites were prepared by a sol-gel method followed by photoreduction. Effect of Ag-AgBr content on the physicochemical properties and antibacterial activities of the Ag-AgBr/TiO2 composites was investigated. These composites showed intrinsic antibacterial activities against Escherichia coli (E. coli) in the dark attributed to the Ag nanoparticles dispersed in the composites. Under visible light irradiation, inactivation of E. coli over these Ag-AgBr/TiO2 composites was attributed to both their photocatalytic disinfection activities and intrinsic antibacterial properties. The Ag-AgBr/TiO2 with an optimum Ti/Ag atomic ratio of 10 exhibited superior visible-light photocatalytic activities for ibuprofen degradation and mineralization as compared to the other Ag-AgBr/TiO2 composites and also Ag-AgBr/P25, Ag/TiO2 and TiO2. It is probably because of the coexistence of two visible-light active components (AgBr and Ag nanoparticles) and the most effective separation of photogenerated electrons and holes in this photocatalyst. Correspondingly, the photocatalyst achieved a much higher efficiency of E. coli destruction than Ag-AgBr/P25 and TiO2. E. coli was almost completely inactivated (7-log reduction) within 60 min by the photocatalyst with a rather low dosage of 0.05 g L(-1) under white LED irradiation. Furthermore, the Ag-AgBr/TiO2 showed high stability for photocatalytic destruction of E. coli and the dark repair and photoreactivation did not occur after the photocatalytic process. Finally, the action spectrum of this photocatalyst for E. coli inactivation and the influence of several inorganic ions present in surface water were also investigated.

Hierarchically plasmonic photocatalysts of Ag/AgCl nanocrystals coupled with single-crystalline WO₃ nanoplates

The hierarchical photocatalysts of Ag/AgCl@plate-WO₃ have been synthesized by anchoring Ag/AgCl nanocrystals on the surfaces of single-crystalline WO₃ nanoplates that were obtained via an intercalation and topochemical approach. The heterogeneous precipitation process of the PVP-Ag⁺-WO₃ suspensions with a Cl⁻ solution added drop-wise was developed to synthesize AgCl@WO₃ composites, which were then photoreduced to form Ag/AgCl@WO₃ nanostructures in situ. WO₃ nanocrystals with various shapes (i.e., nanoplates, nanorods, and nanoparticles) were used as the substrates to synthesize Ag/AgCl@WO₃ photocatalysts, and the effects of the WO₃ contents and photoreduction times on their visible-light-driven photocatalytic performance were investigated. The techniques of TEM, SEM, XPS, EDS, XRD, N₂ adsorption-desorption and UV-vis DR spectra were used to characterize the compositions, phases and microstructures of the samples. The RhB aqueous solutions were used as the model system to estimate the photocatalytic performance of the as-obtained Ag/AgCl@WO₃ nanostructures under visible light (λ ≥ 420 nm) and sunlight. The results indicated that the hierarchical Ag/AgCl@plate-WO₃ photocatalyst has a higher photodegradation rate than Ag/AgCl, AgCl, AgCl@WO₃ and TiO₂ (P25). The contents and morphologies of the WO₃ substrates in the Ag/AgCl@plate-WO₃ photocatalysts have important effects on their photocatalytic performance. The related mechanisms for the enhancement in visible-light-driven photodegradation of RhB molecules were analyzed.