Photochemical Reduction Process Research Articles

An Innovative Approach for Precise Identification of the Lowest Unoccupied Molecular Orbital Using the Parametric Equation of Motion.

The lowest unoccupied molecular orbital (LUMO) plays a crucial role in quantum chemistry, but current quantum chemistry calculations fail to provide useful virtual orbitals, making it challenging to explore various processes such as photochemical reactions, electron attachment, reduction, or excitation processes. The LUMO obtained from the self-consistent field (SCF) solution can not be relied upon and needs to be identified as they are often present among the continuum states having almost similar energies. The nuclear charge stabilization method has been proven useful in identifying LUMO. Herein, we have proposed the application of parametric equations of motion (PEM) in conjunction with nuclear charge stabilization method to identify the LUMO obtained from the SCF solution exhibiting stability with different basis sets including diffuse functions.

A More Controllable Laser Reduction of Graphene Oxide Membrane for Electrode Applications

Reduced graphene oxide (rGO) has attracted significant attention as an active electrode material for sensors and flexible energy devices due to its high electric conductivity and large surface area. rGO is usually obtained from graphene oxide(GO) through a thermal, chemical, photochemical, and electrochemical reduction process. Compared to the other reduction strategy, laser reduction is a single-step, precise, low cost, and chemical-free processing that can be directly applied on the GO membrane at room temperature in an ambient condition.The laser irradiation parameter, such as laser source, power, speed, and frequency, plays an important role in reduction optimization. In general, the quality of the rGO is not as high as that of pristine graphene because of incomplete reduction, and oxygenated defects involved in the reduction process.The not fully removed oxygenated function group not only influence the sensitivity and selectivity of the electrode, but also influences response time and recovery time during sensing and the electrochemical window of the supercapacitor made with those rGO electrode.This study aims to develop reduced graphene oxide (rGO) through laser irradiation for application in supercapacitors and electrochemical sensors as electrodes. GO membranes were fabricated with a layer-by-layer assembly process first then further reduced through conventional CO2 laser reduction. The laser irradiation parameters including intensity, frequency, and scan speed will be optimized to achieve the reduction up to maximi, C/O ratio. The effects of the reduction will be characterized and evaluated using scanning electron microscope (SEM), Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD)spectroscopy, and four-point probe station. The influence of the humidity on the impedance of the rGO electrode and the capacitance of the planar supercapacitor made with rGO electrode will also be analyzed for potential application of as-prepared rGO electrodes in supercapacitors and humidity sensors.

Molecular engineering of biomimetic donor-acceptor conjugated microporous polymers with full-spectrum response and an unusual electronic shuttle for enhanced uranium(VI) photoreduction

Realizing an efficient photochemical uranium reduction process using metal-free conjugated polymers is highly desirable, but is extremely challenging, as it requires a broad photo-response range and efficient electron transmission channels. Herein, three novel full-spectrum (200 ≤ λ ≤ 800 nm) responsive biomimetic donor–acceptor conjugated microporous polymers (CMPs) were successfully constructed to photoreduce uranium through a molecular engineering strategy. The optical band gap and built-in electric field of the CMPs were conveniently optimized via various quinone-containing acceptors. Furthermore, the quinone-containing block exhibited outstanding redox activity, which could serve as an unique electron shuttle to rapidly transfer electrons. Consequently, ECUT-TQ with 2,6-dibromobenzo[1,2-b:4,5-b']dithiophene-4,8-dione block exhibits a narrow band gap as low as 1.70 eV, a stronger built-in electric field and more efficient charge separation, achieving 97.4% photocatalytic U(VI) reduction efficiency with a photoreaction rate constant of 0.057 min−1. The exhaustive mechanism analysis illustrates that the dominant active species in the photocatalytic process where U(VI) is reduced to UO2 are photoelectrons and •O2– radicals. This work provides a novel approach for designing high-performance green biomimetic photocatalysts for removing radioactive pollution.

A New Medical Dressing with Silver Nanoparticles to Treat Diabetic Foot Patient

In this study, we prepared medical dressings with silver nanoparticles to treat diabetic foot patient by photochemical reduction process of silver ions using sodium citrate and UV radiation. Antibacterial activity of dressing with silver nanoparticles against bacteria associated with diabetic foot was studied by disk diffusion method. It was observed that the bacteria did not grow on the culture medium where the medical gauze was impregnated with silver nanoparticles.

SnSxSe1–x/Ag Nanosheet Thin Films for Solar Energy Water Splitting

Earth-abundant and ecofriendly minerals SnSxSe1–x can be promising candidates for photoelectrochemical (PEC) cells because of their tunable band gaps and high absorption efficiency. Metal nanoparticle-modified SnSxSe1–x enhance the efficiencies of solar energy water splitting. In this paper, SnSxSe1–x nanosheets (NSs) were prepared by a one-pot method and silver (Ag) nanoparticles were deposited on the surface of SnSxSe1–x NSs through a photochemical reduction process. The structural properties of SnSxSe1–x and SnSxSe1–x/Ag NSs were characterized by X-ray diffraction (XRD) and Raman spectroscopy. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the morphologies of SnSxSe1–x and SnSxSe1–x/Ag NSs. The band gaps of SnSxSe1–x and SnSxSe1–x/Ag NSs were determined using the UV–Vis–NIR spectra. PEC measurements indicated that the photocurrents of SnSxSe1–x thin films increased first and then decreased with the increase of Se. The SnS0.5Se0.5 thin films had the best PEC properties. The modification of Ag nanoparticles enhanced the PEC properties of SnSxSe1–x NSs. The highest photocurrent density of 69.3 μA/cm2 and the incident monochromatic photon-to-electron conversion efficiency (IPCE) of 27.9% were obtained.

Metal-Free Catalysis: A Redox-Active Donor-Acceptor Conjugated Microporous Polymer for Selective Visible-Light-Driven CO2 Reduction to CH4.

Achieving more than a two-electron photochemical CO2 reduction process using a metal-free system is quite exciting and challenging, as it needs proper channeling of electrons. In the present study, we report the rational design and synthesis of a redox-active conjugated microporous polymer (CMP), TPA-PQ, by assimilating an electron donor, tris(4-ethynylphenyl)amine (TPA), with an acceptor, phenanthraquinone (PQ). The TPA-PQ shows intramolecular charge-transfer (ICT)-assisted catalytic activity for visible-light-driven photoreduction of CO2 to CH4 (yield = 32.2 mmol g-1) with an impressive rate (2.15 mmol h-1 g-1) and high selectivity (>97%). Mechanistic analysis based on experimental results, in situ DRIFTS, and computational studies reveals that the potential of TPA-PQ for catalyzing photoreduction of CO2 to CH4 was energetically driven by photoactivated ICT upon surface adsorption of CO2, wherein adjacent keto groups of PQ unit play a pivotal role. The critical role of ICT for stimulating photocatalysis is further illustrated by synthesizing another redox-active CMP (TEB-PQ), bearing triethynylbenzene (TEB) and PQ, that shows 8-fold lesser activity for photoreduction toward CO2 to CH4 (yield = 4.4 mmol g-1) as compared to TPA-PQ. The results demonstrate a novel concept for CO2 photoreduction to CH4 using an efficient, sustainable, and recyclable metal-free robust organic photocatalyst.

Solar-driven conversion of carbon dioxide over nanostructured metal-based catalysts in alternative approaches: Fundamental mechanisms and recent progress

Solar-driven carbon dioxide (CO2) conversion has gained tremendous attention as a prominent strategy to simultaneously reduce the atmospheric CO2 concentration and convert solar energy into solar fuels in the form of chemical bonds. Numerous efforts have been devoted to diverse photo-driven processes for CO2 conversion, which utilized a multidisciplinary strategy. Among them, the architecture of nanostructured metal-based catalysts is emerging as an eminent solution for the design of catalysts of this field. In this work, we first provide fundamental mechanisms of photochemical, photoelectrochemical, photothermal, and photobio(electro)chemical CO2 reduction processes to achieve an in-deep understanding of vital aspects. Importantly, the recent progress in the catalyst design for each reaction system is discussed and highlighted. Based on these analyses, an overview of photo-driven CO2 reduction on metal-based catalysts for solar fuel production is also spotlighted. Finally, we analyze challenges and prospects for the strategic direction of developments in the field.

Synthesis of SnS:Ag nanosheets for solar energy water splitting

In this paper, tin monosulfide (SnS) nanosheets were prepared by one-pot method and silver (Ag) nanoparticles (NPs) were deposited on the SnS nanosheets (NSs) through a photochemical reduction process. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and energy spectrometer (EDS), UV–Vis-NIR diffuse reflectance spectroscopy were used to characterize the physical properties of the SnS:Ag NSs. Photoelectrochemical tests indicated that Ag NPs enhanced the photoelectric properties of SnS NSs and the highest photocurrent density of 14.93 μA/cm2 was achieved.

A functional Ag-TiO2 nanocomposite solar selective absorber with antimicrobial activity by photochemical reduction process

A functional nanocomposite coating developed by wet chemical route in a photochemical reduction process will be a good candidate for low temperature solar thermal application. The low-temperature curable cermet comprises of two different type of nanoparticles, generated by photocatalytic reduction of silver ions under the sunlight with the aid of crystalline TiO2 (~8 nm) nanoparticles. The optimized base absorber layer of Ag-TiO2 nanocomposite exhibited absorptance (α) of 0.90 and emittance (ε) of 0.18 at 200 °C. Further to improve the optical properties a second layer of MgF2 has been added to get high selective (α/ε = 0.93/0.19 at 200 °C) nature. In addition, the coating was demonstrated to possess an antimicrobial activity against both Gram-negative and Gram-positive bacteria. The presented work will provide a new insight into the spectrally selective absorbers and its antimicrobial nature, which may useful for water disinfection, hot water, industrial heating and swimming pool applications.

Ag@CoFe2O4/Fe2O3 nanorod arrays on carbon fiber cloth as SERS substrate and photo-Fenton catalyst for detection and degradation of R6G

In this study, Ag nanoparticles loaded CoFe2O4/Fe2O3 nanorod arrays on carbon fiber cloth have been successfully fabricated by a hydrothermal route followed by a calcination treatment and photochemical reduction process. The as-prepared composite has been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The obtained Ag@CoFe2O4/Fe2O3 nanorod arrays show excellent SERS performance, which provides enhancement factors (EF) as high as about 1.2 × 108 for Rhodamine 6G (R6G). The SERS signals collected over a 20 µm × 20 µm area show relative standard deviation lower than 12%, suggesting good SERS signal uniformity. In addition, the Ag@CoFe2O4/Fe2O3 nanorod arrays can be used as an effective photo-Fenton catalyst photocatalytical degradation of R6G. It was found that 99.15% of R6G can be degraded in an hour. This bifunctional composite that can act both as SERS substrates and as photo-Fenton catalyst would facilitate the cleaning and recycling of SERS substrates for reusing through a photocatalytic process, as well as facilitate the integration of rapid detection and effective degradation of organic pollutants.

Immobilization of plasmonic Ag-Au NPs on the TiO2 nanofibers as an efficient visible-light photocatalyst

A heterostructure photocatalyst including metallic silver (Ag), gold (Au) in the form of nanoparticles (NPs) and titanium oxide (TiO2) nanofibers were fabricated using a combination of photodeposition and electrospinning techniques. In this procedure, electrospun TiO2 nanofibers were decorated by plasmonic Ag and Au NPs on the surface of nanofibers which were generated via photochemical reduction process. The synthesized Ag-Au/TiO2 nanocomposites which were considered as a favorable candidate for enabling the more access to visible-light in photocatalytic performance were subsequently characterized by field emission scanning electron spectroscopy (FESEM), transmission electron spectroscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and ultra-violet-visible (UV–vis) spectroscopy. UV–vis studies indicate the extension in the absorption region of composite toward the visible-light range have been occurred through the loading metallic nanoparticles into the TiO2 structure. Microscopic assessments in addition to EDS revealed that metallic NPs deposited on the surface of the fibers through photochemical reduction process. It was found that, the ratio of utilized Ag/Au in the final composite can significantly enhance the photocatalytic efficiency. It was suggested that introduction of the proper amount of noble metal NPs into the TiO2 matrix leads to the notable enhancement of visible-light decomposition of rhodamine B (Rh. B) as a model dye.

Sulfite promoted photochemical cleavage of s-triazine ring: The case study of atrazine

Regarding the abundant solar energy on the earth, photochemical method is the most attractive approach for the decomposition of atrazine pollutant which is widely existed in surface water. In this study, we report that the presence of sulfite can alter the photochemical atrazine degradation pathway to cleave its s-triazine ring. Density functional theory calculation results first suggested that a reductive process might be highly possible to break the s-triazine ring of atrazine by comparing the highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap values of six possible atrazine degradation intermediates. The subsequent experimental results reveal that the presence of sulfite shifted a direct atrazine hydroxylated dechlorination pathway to an indirect photo-degradation route with the aid of hydrated electrons and hydrogen atoms, which were produced from the photolysis of sulfite solution under UV irradiation. This rational degradation pathway change increased the atrazine degradation and dechlorination rates by 4.3times, and also effectively cleaved s-triazine ring, as confirmed by the generation of ammonium ions and small molecule acids during the degradation of 2,4-diamino-1,3,5-triazine with this sulfite promoted photochemical reduction process. This study provides a mild strategy to completely mineralize atrazine, and also sheds light on how the degradation pathway could affect the s-triazine ring cleavage.

Enhanced Catalytic Reduction of p-Nitrophenol on Ultrathin MoS2 Nanosheets Decorated with Noble Metal Nanoparticles

In this work, ultrathin MoS2 nanosheets (MoS2 NSs) with defect-rich structure were prepared and used as catalysts for the reduction of p-nitropheonol. Also, thanks to the defect sites, noble metal (Au, Ag, Pd, Pt) nanoparticles (NPs) can be successfully deposited on the MoS2 NSs via a facile and efficient one-step photochemical reduction process without the assistance of a stabilizer. The morphology and crystal structure of as-synthesized materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and N2 physisorption mearurements. Catalytic results demonstrate that as-prepared MoS2 NSs and noble metal modified MoS2 NSs (NM/MoS2 NSs) effectively catalyze the reduction of p-nitrophenol (p-NP) to p-aminophenol (p-AP) with NaBH4. The Pd/MoS2 NSs shows the best catalytic performance, exhibiting an apparent rate constant (κapp) of 0.386 min–1 even with moderate chemical stability. Interestingly, the...

Plasmonic Ag-TiO2 − x nanocomposites for the photocatalytic removal of NO under visible light with high selectivity: The role of oxygen vacancies

Integration of semiconductors with plasmonic noble metal nanoparticles for visible- light driven photocatalysis has become an interesting research field recently. In this work, Ag-TiO2−x nanocomposites were successfully synthesized via a facile photochemical reduction process followed by post-annealing. The deposition of Ag nanoparticles greatly increases the light absorption and charge separation. Compared with commercial P25, the Ag-TiO2−x nanocomposites are not only superior in visible-light photocatalytic NO removal, but also in inhibiting the production of NO2, whose toxicity is 4–5 times higher than NO. As confirmed by gas chromatography, the photo-oxidation of NO and selective photo-reduction of NO to N2 occur simultaneously during the process of NO removal by Ag-TiO2−x. The oxidation of NO was due to the synergic effect between h+ and O2−; while the selective photo-reduction was resulted from introduced oxygen vacancies in TiO2. In addition, the light wavelength dependence measurement reveals that the surface plasmon resonance effect of Ag is responsible for the improvement of the visible-light photoactivity. The present study will provide an alternative approach to design highly selective photocatalysts for NO removal under visible-light.

A new form of chemisorbed photo- and electro-active atomic H species on the TiO2(110) surface

Hydrogen adsorption on TiO2 is of importance in chemical and photochemical reduction processes. Using several surface science methods, we clearly distinguish two kinds of H species on the surface of rutile TiO2(110)-1×1. In contrast with the well-studied bridge-bonded OH species (α-H) originating from H2O dissociation on the surface oxygen vacancy site on TiO2(110), atomic H adsorption on the TiO2(110) (denoted as β-H) exhibits special high sensitivity to the electronic excitation of the TiO2(110) by either electrons or UV photons. The formation of molecular H2 gas by photoexcitation of β-H/TiO2(110) surfaces has been observed, which may shed light on the basic understanding of the processes of photocatalytic H2 production by splitting water.

Predicting growth of gold nanoparticle by photochemical reduction process associated with mathematical modelling

Nowadays, to develop new generation of nanodevices, most researchers such as chemists, physicists, biologists, even the engineers are focusing their studies towards the uniqueness as well as the chemical properties of metal nanoparticles. Even, the mathematician also has governed the appropriate mathematical modelling regarding of properties of nanoparticles such as gold nanoparticles. In this paper, some experiment regarding the photochemical and photocatalytic processes for predicting the growth of gold nanoparticles from previous studies has been reviewed. Besides that, in observing the growth rate of gold nanoparticles, a mathematical modelling has been governed. Where, ultraviolet, UV radiation with wavelength of 366 nm and 253.7 nm has been fixed as the constant parameters. The governing equation is then solved numerically using some iterative method known as Jacobi and Gauss Seidel. The convergence of both methods is discussed in detail and the numerical analysis is presented in table form to justify and validate the convergence as well as the performance of the proposed iterative methods.

Ternary reduced-graphene-oxide/Bi2MoO6/Au nanocomposites with enhanced photocatalytic activity under visible light

A novel ternary nanocomposite photocatalyst consisted of reduced-graphene-oxide (RGO), Bi2MoO6 and plasmonic Au nanoparticles were successfully fabricated by multiple steps including a simple solvothermal process and photochemical reduction process. RGO/Bi2MoO6/Au was characterized by X-ray powder diffraction patterns, transmission electron microscopy, UV–vis diffuse reflectance spectra, Raman spectroscopy and X-ray photoelectron spectroscopy. In comparison with Bi2MoO6, RGO/Bi2MoO6 and Au/Bi2MoO6, RGO/Bi2MoO6/Au exhibits an enhanced photocatalytic activity for decomposition of Rhodamine B under visible light. The separation efficiency of the photogenerated holes and electrons on Bi2MoO6 is promoted by the combined effect of both RGO and Au in the ternary composite, and thus enhances photocatalytic activity. The scavenger study revealed that both hole and superoxide are the major reactive species for the photocatalytic degradation of Rhodamine B using RGO/Bi2MoO6/Au photocatalyst.

Ag-decorated K2Ta2O6 nanocomposite photocatalysts with enhanced visible-light-driven degradation activities of tetracycline (TC)

In this paper, octahedral K2Ta2O6 nanocrystals have been synthesized by a single-step hydrothermal method. Then the visible-light-driven plasmonic Ag–K2Ta2O6 nanocomposite photocatalysts are prepared by a photochemical reduction process. The product was characterized using various techniques, such as X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), UV–visible diffuse-reflectance spectroscopy (DRS). The results show that the Ag nanoparticles are uniformly loaded on the surface of the K2Ta2O6. The prepared Ag–K2Ta2O6 exhibits an efficient photocatalytic activity for degradation of tetracycline (TC) under visible-light irradiation and shows good repeatability and stability. In particular, the highest photocatalytic activity at the nominal atomic ratio of silver to tantalum as 3%, which is more than 3 times that of pure K2Ta2O6.

Thermal and Photoinduced Reduction of Ionic Au(III) to Elemental Au Nanoparticles by Dissolved Organic Matter in Water: Possible Source of Naturally Occurring Au Nanoparticles

Naturally occurring Au nanoparticles (AuNPs) have been widely observed in ore deposits, coal, soil, and environmental water. Identifying the source of these naturally occurring AuNPs could be helpful for not only the discovery of Au deposits through advanced exploration methods, but also the elucidation of the biogeochemical cycle and environmental toxicity of ionic Au and engineered AuNPs. Here, we investigated the effect of natural/simulated sunlight and heating on the reduction of ionic Au by ubiquitous dissolved organic matter (DOM) in river water. The reductive process probed by X-ray photoelectron spectroscopy revealed that phenolic, alcoholic, and aldehyde groups in DOM act as reductive sites. Long-time exposure with thermal and photoirradiation induced the further fusion and growth of AuNPs to branched Au nanostructure as precipitation. The formation processes and kinetics of AuNPs were further investigated using humic acid (HA) as the DOM model, with comprehensive characterizing methods. We have observed that HA can reduce ionic Au(III) complex (as chloride or hydroxyl complex) to elemental Au nanoparticles under sunlight or heating. In this process, nearly all of the Au(III) could be reduced to AuNPs, in which HA serves as not only the reductive agent, but also the coating agent to stabilize and disperse AuNPs. The size and stability of AuNPs were highly dependent on the concentration ratio of Au(III) to HA. These results imply that, besides biological processes, this thermal or photochemical reduction process is another possible source of naturally occurring AuNPs in natural environments, which possibly has critical impacts on the transport and transformation of Au and engineered AuNPs.

Enhanced visible-light photocatalytic activity of plasmonic Ag and graphene co-modified Bi2WO6nanosheets

Photocatalytic degradation of pollutants in water has received much attention due to increasing environmental problems. In this study, a visible-light-driven plasmonic silver-graphene-bismuth tungsten (Ag-G-Bi2WO6) composite photocatalyst was prepared. Firstly, the graphite oxide (GO)-Bi2WO6 composite was prepared using a hydrothermal process, followed by a chemical reduction process using ethyl glycol (EG) as the reducing agent to form the G-Bi2WO6 composite. Then, Ag nanoparticles (NPs) were loaded onto the G-Bi2WO6 composite using a simple photochemical reduction process under xenon lamp irradiation to form the Ag-G-Bi2WO6 composite. The prepared samples were characterized using X-ray diffraction, transmission electron microscopy, nitrogen adsorption-desorption isotherm, UV-visible diffuse reflectance spectroscopy and electrochemical impedance spectroscopy. The photocatalytic activities of the prepared samples were evaluated by the photocatalytic degradation of rhodamine B (RhB) aqueous solution at ambient temperature under visible-light irradiation. The results showed that the photocatalytic activity of Bi2WO6 was significantly enhanced by the loading of Ag and graphene. The high photocatalytic activity is attributed predominantly to the hybridization of the surface plasmonic resonance (SPR) effect of Ag NPs and the specific electronics effect of graphene on the Bi2WO6 surface, thus enhancing the generation and separation of photogenerated charge carriers of Bi2WO6. Meanwhile, the excellent adsorption capacity of graphene also contributes to the enhancement of photocatalytic activity. This work highlights the design and preparation of new photocatalysts using plasmonic Ag and graphene as cocatalyst.