Visible-light Reaction Research Articles

Graphitic Carbon Nitride Based Semiconductors and Their Applications in the Field of Photocatalysis

An increasing number of advanced semiconductor materials have been reported with the progress of theoretical and practical researches. The graphitic carbon nitride (g-C3N4) stands out as a highly promising semiconductor photocatalyst. It is known for its visible-light reaction and good chemical stability, indicating its potential for extensive use in photocatalysis. Recently, rapid progress has been made in researching g-C3N4-based semiconductor substances in photocatalysis. Till now, a large amount of work has focused on the applications of g-C3N4 in photocatalysis. This work focuses on those researches concerning with g-C3N4-based photocatalytic substances. Their structural characteristics, synthesis techniques, and efficiency enhancement are discussed in detail. Besides, their applications in different photocatalytic reactions are also highlighted. These reactions include hydrogen production by water decomposition, degradation of organic matter, carbon dioxide reduction, and photocatalytic bactericide. This article also points out the problems and challenges in the photocatalytic performance. Meanwhile, the stability of g-C3N4 is also highlighted. It also puts forward the promising research directions of g-C3N4 in the field of photocatalysis.

Ultrafast Processes in Upper Excited Singlet States of Free and Caged 7-Diethylaminothiocoumarin.

The photochemistry and photophysics of thiocarbonyl compounds, analogues of carbonyl compounds with sulfur, have long been overshadowed by their counterparts. However, recent interest in visible light reactions has reignited attention toward these compounds due to their unique excited-state properties. This study delves into the ultrafast dynamics of 7-diethylaminothiocoumarin (TC1), a close analogue of the well-known probe molecule coumarin 1 (C1), to estimate intersystem crossing rates, understand the mechanisms of fluorescence and phosphorescence, and evaluate TC1's potential as a solvation dynamics probe. Enclosing TC1 within an organic capsule indicates its potential applications, even in aqueous environments. Ultrafast studies reveal a dominant subpicosecond intersystem crossing process, indicating the importance of upper excited singlet and triplet states in the molecule's photochemistry. The distinct fluorescence and phosphorescence origins, along with the presence of closely spaced singlet excited states, support the observed efficient intersystem crossing. The sulfur atom alters the excited-state behavior, shedding light on reactive triplet states and paving the way for further investigations.

Fabrication of Ag3PO4/N-doped TiO2 nanotubes heterojunction photocatalysts for visible-light-driven photocatalysis

As an environmentally friendly and energy-efficient technology, photocatalysis holds considerable potential for eliminating organic pollutants. In this study, novel visible-light-driven Ag3PO4-decorated nitrogen-doped TiO2 nanotubes (Ag3PO4/N-TNTs) photocatalysts with advanced properties of heterostructures were successfully synthesized and used to degrade methylene blue (MB) dye. The fabrication of Ag3PO4/N-TNTs photocatalysts involved a two-step electrochemical anodization to obtain TiO2 nanotubes (TNTs) and the wet impregnation of the amorphous tubular structure in NH3 solution, followed by calcination in air to obtain crystallized nitrogen-doped TiO2 nanotubes (N-TNTs). Finally, the decoration of the N-TNTs with Ag3PO4 nanoparticles was conducted to enhance visible-light reactivity. Various heterojunction photocatalysts were obtained by changing the concentration of NH3 (0.5–2.5 M) and the dosage of Ag3PO4 (0.25–1.5 wt%) in the composites. Results of ultraviolet–visible (UV–Vis) absorption, photocurrent transient, and electrochemical impedance spectroscopy measurement revealed that Ag3PO4/N-TNTs possessed a significant response in the visible-light range and good photoelectronic properties. The superior photocatalytic activity of the Ag3PO4/N-TNTs catalyst was achieved under the optimal conditions of N-doping using 2-M NH3 and Ag3PO4 deposition at a dosage of 0.75 wt%. Based on the degradation efficiency (DE) of MB, the optimal Ag3PO4/N-TNTs exhibited rate constants of 4.5 and 2 times higher than those of the pristine TNTs and N-TNTs, respectively. The high stability of Ag3PO4/N-TNTs was confirmed through four cycles of reutilization, with a small decay of only 5.3% in the DE of MB dye for each run of photocatalysis. The scavenger tests of generated reactive oxygen species revealed that ·OH and ·O2− were the primary contributors to photocatalytic performance. The synthesized Ag3PO4/N-TNTs heterostructure photocatalysts were proven to possess efficient separation of photogenerated charge carriers, high reactivity, and stability in the visible-light region.

Hydroxy- and Hydro-Perfluoroalkylation of Styrenes by Controlling the Quenching Cycle of Eosin Y.

Fluoroalkyl compounds are widely used, underscoring a pressing need for the development of methods for their synthesis. However, reports on perfluoroalkylation to styrenes have been sparse. In this study, both hydroxy- and hydro-perfluoroalkylation of styrene were achieved using visible light reactions, catalyzed by eosin Y, by selecting appropriate additives and controlling the eosin Y quenching cycle. These reactions are heavy-metal free, use water as the hydroxyl or hydrogen source, and employ inexpensive and readily available reagents.

Mint powder assisted synthesis of CQDs/BiOCl with tunable OVs and improved photocatalytic property

Development of advanced technologies for the removal of perfluorooctanoic acid (PFOA) from waterbody has been a challenge because of the persistent, widely distributed and potentially toxic nature of PFOA in the aquatic environment as well as the high binding energy of C-F bond, therefore, it is difficult to remove PFOA by routine heating, ultraviolet radiation and biological degradation. In this study, BiOCl-based photocatalysts containing carbon quantum dots (CQDs) with visible light reactivity were prepared by a hydrothermal approach using mint powder (MNP) as raw material for CQDs. The prepared samples exhibit self-assembled three dimensions(3D) flower-like microspheres with adjustable oxygen vacancies (OVs). The experimental results show that the activity of BiOCl modified with CQDs is significantly increased compared to that of the reference BiOCl. When the mass ratio of MNP/BiOCl is 2%, the 2% CQDs/BiOCl photocatalyst shows a three-fold enhancement in degradation activity toward destruction of rhodamine (RhB) compared with the reference BiOCl under visible light irradiation. Additionally, degradation activity of 2% CQDs/BiOCl catalyst toward decontamination of PFOA under UV light irradiation also increases. This presentation offers a robust strategy for the synthesis of significantly efficient photocatalysts for detoxification of the organic pollutants.

Visible light-regulated thermal catalytic selectivity induced by nonthermal effects over CuNi/CeO2

Solar-assisted photothermal catalysis is a fascinated picture of chemical and energy conversion. However, it is difficult to distinguish the nonthermal effects due to the thermal and nonthermal tend to exhibit similar experimental results. Here, we reported that the CuNi alloy deposited CeO2 (CuNi/CeO2) with visible light excited carriers at the interface can promote CO2 reduction in the photothermal catalysis. Impressively, the CuNi/CeO2 exhibit different product selectivities in the dark and visible light reactions, especially the light promoted the further hydrogenation to CH4 conversion. Detailed experiments reveal that the hot electron transfer between plasmon metal Cu and metal Ni under visible light excitation alters the pathway of thermal reduction while increasing surface hydroxyl and oxygen vacancies as CO2 trapping sites. The excessive H2 activation under visible irradiation induces the deep reduction of CO2 to CH4, instead of reverse water gas shift. Combining with in-situ DRIFTS, quasi-situ EPR, H2 pulse and DFT calculations, the nonthermal effects of CO2 reduction is proposed over CuNi/CeO2 with electrons transfer between Cu and Ni nanoparticles.

Decoupling the effects of defects on efficiency and stability through phosphonates in stable halide perovskite solar cells

Summary Understanding defects is of paramount importance for the development of stable halide perovskite solar cells (PSCs). However, isolating their distinctive effects on device efficiency and stability is currently a challenge. We report that adding the organic molecule 3-phosphonopropionic acid (H3pp) to the halide perovskite results in unchanged overall optoelectronic performance while having a tremendous effect on device stability. We obtained PSCs with ∼21% efficiency that retain ∼100% of the initial efficiency after 1,000 h at the maximum power point under simulated AM1.5G illumination. The strong interaction between the perovskite and the H3pp molecule through two types of hydrogen bonds (H…I and O…H) leads to shallow point defect passivation that has a significant effect on device stability but not on the non-radiative recombination and device efficiency. We expect that our work will have important implications for the current understanding and advancement of operational PSCs.

Effect of Cu, Cr, S Doped TiO2 for Transparent Plastic Bar Reinforced Concrete

In this study, after firing and powdering Cu, Cr, and S with NP-400 TiO2, an NOx removal rate test was performed according to the ISO test method to analyze the photocatalytic reactivity in visible light. The distribution of the photocatalyst and visible light reactivity on the surface of the test specimen were confirmed through SEM (Scanning electron microscope), EDS (Energy dispersive spectroscopy), XRD (X-ray diffraction), UV-visible absorption spectrum and energy band gap tests. The flowability of UHPC (Ultra high performance concrete) slightly decreased due to the increase in the photocatalyst mixing rate, but both J-Ring and L-Box test results showed that there is no problem when concrete is placed. As a result of SEM and EDS tests, good microstructure and peak values were confirmed in the test specimens doped with Cu, and as a result of the XRD test, anatase and rutile peaks were confirmed in the Cu, Cr, and S specimens. In the UV-visible absorption spectrum analysis, it was confirmed that only the specimen doped with Cu maintains a high absorption power of 0.8 up to 700 nm, and the inherent band gaps are reduced to 2.9 eV, thereby increasing the possibility of reaction in visible light. Finally, as a result of the NOx removal test by the ISO test method, about 15.8% was removed for 5 h in the specimen doped with Cu, and the removal efficiency is estimated to be possible up to about 25% when applied with the TPBRC (transparent plastic bar reinforced concrete).

Photocatalytic behavior of biochar-modified carbon nitride with enriched visible-light reactivity

Ultra-thin layered structures and modified bandgaps are two efficient strategies to increase the photocatalytic performance of various materials for the semiconductor industry. In the present study, we combined both strategies in one material to form carbon-doped graphitic carbon nitride (g-C3N4) nano-layered structures by the method of melamine thermal condensation, in the presence of different mass ratios of biochar. The characterization showed that the composite with the best ratio retained the g-C3N4 polymeric framework and the bond with g-C3N4. The biochar was established via π-π stacking interactions and ether bond bridges. The π-conjugated electron systems provided from biochar can elevate charge separation efficiency. The ultra-thin structure also curtailed the distance of photogenerated electrons migrating to the surface and enlarge specific surface area of materials. The presence of carbon narrowed the bandgap and increased light absorption at a wider range of wavelengths of g-C3N4. The biochar/melamine ratio of 1:15 presented the best performance, 2.8 and 5 times faster than g-C3N4 degradating Rhodamine and Methyl Orange, respectively. Moreover, the catalyst presented a good stability for 4 cycles. In addition to that, biochar from waste biomass can be considered a sustainable, cost-effective, and efficient option to modify g-C3N4-based photocatalysts.

Understanding the characteristics, enhanced optical and photoelectrochemical performance of copper-loaded titania nanotubes synthesized via successive ionic layer adsorption reaction

The physico-chemical, optical and photoelectrochemical (PEC) characteristics of copper sensitized titania nanotubes (CuTNT) nanocomposites are still not well understood despite numerous conducted studies. In the present study, copper sensitized titania nanotubes (CuTNT) were prepared using customized Successive Ionic Layer Adsorption Reaction (SILAR) method. The foremost aim is to investigate the aforestated characteristics and consolidate the results to propose mechanisms to elucidate CuTNT’s enhanced optical and PEC performance. Such mechanisms are of particular interest because a better understanding of them would essentially translate to advances in improved CuTNT production and use, especially in regard to PEC applications. We, therefore, attempt to shed more light on its characteristics by employing electron microscopies, X-ray powder diffraction and X-ray photoelectron spectroscopy techniques. Well-ordered crystalline TNT was successfully obtained via anodization in the mixture of ethylene glycol and water mixed with NH4F. CuTNTs were prepared at various concentrations, SILAR cycles and immersion times. CuTNT/20 min of fixed 20 mM and 3 SILAR cycles showed enhanced photoconversion efficiency of almost 2.7 times higher compared to pure TNT due to electron-trap center effect introduced by Cu, reduced band gap energy from 3.26 eV of pure TNT to 2.75 eV, enhanced visible light reactivity and balanced distribution within TNT.

Visible light driven hydrogen evolution by photocatalytic reforming of lignin and lactic acid using one-dimensional NiS/CdS nanostructures

Uniform one-dimensional (1D) NiS/CdS nanocomposites have been fabricated using CdS nanowires (NWs) and NiS nanoparticles as building blocks through two-pot solvothermal synthesis. The synergistic interaction between CdS and NiS, stemming from their intimate contact, efficiently enhanced charge carrier separation, with the NiS, as a non-noble metal cocatalyst, enriching the active sites for H2 production from water. Consequently, compared with pristine CdS NWs, the 1D NiS/CdS nanocomposite exhibited improved visible light reactivity in the generation of H2. The activity of NiS/CdS with 20 mol% of NiS loading, under the coexistence of lactic acid and lignin as hole scavengers, is 5041 times that of pristine CdS, with an apparent quantum efficiency (AQE) of 44.9% for H2 generation. To gain deeper insight into the mechanism behind the enhanced performance, ultrafast dynamics studies based on femtosecond transient absorption (TA) techniques have been applied to probe the charge carrier dynamics. The results reveal that presence of 0.2 molar ratio of NiS improved the average charge carrier lifetime of CdS NWs by 97 times, potentially leading to more efficient charge separation and transfer. However, further increasing the NiS loading resulted in shorter lifetime or faster electron-hole recombination, attributed to aggregation of NiS nanoparticles. The dynamics results agree well with the photocatalytic results in that the longer charge carrier lifetime correlates with improved performance in hydrogen evolution. This work demonstrates a simple approach to controlled synthesis of well-shaped 1D nanocomposite photocatalysts for visible-light driven energy conversion, particularly involving the use of biomass.

Effects of B site doping on electronic structures of InNbO4 based on hybrid density functional calculations

In order to improve the photocatalytic activity under visible-light irradiation, we adopted first principle calculations based on density functional theory (DFT) to calculate the electronic structures of B site transition metal element doped InNbO4. The results indicated that the complete hybridization of Nb 4d states and some Ti 3d states contributed to the new conduction band of Ti doped InNbO4, barely changing the position of band edge. For Cr doping, some localized Cr 3d states were introduced into the band gap. Nonetheless, the potential of localized levels was too positive to cause visible-light reaction. When it came to Cu doping, the band gap was almost same with that of InNbO4 as well as some localized Cu 3d states appeared above the top of VB. The introduction of localized energy levels benefited electrons to migrate from valence band (VB) to conduction band (CB) by absorbing lower energy photons, realizing visible-light response.

Metal-binding hydrazone photoswitches for visible light reactivity and variable relaxation kinetics.

The range of applications for photoswitching moieties is diverse, and the ability to design switches with variable photochemical and physical properties is consequently important for realizing their potential. Previously we reported on the photochromism of (E)-N'-(1-(2-hydroxyphenyl)ethylidene)isonicotinohydrazide (HAPI), an aroylhydrazone compound first developed as a transition metal chelator. Herein we report the synthesis of structurally related aroylhydrazone chelators and explore the effect of these modifications on their UVA, UVC and blue light photoreactivity, photostationary state composition, photoisomer thermal stability, and relative iron(iii) binding affinity. These findings will inform the next generation of aroylhydrazone photoswitches for metal-gated photoswitching applications.

Visible light-induced cis/trans isomerization of dicarbonyl Fe(II) PNP pincer complexes

The synthesis and characterization of dicarbonyl Fe(II) PNP pincer complexes of the type cis-[Fe(PNP-iPr)(CO)2(X)]+ (X=Br, Cl) is described. These complexes are slowly formed when solutions of complexes trans-[Fe(PNP-iPr)(CO)2(X)]+ are kept in the dark for 9h (X=Br) and 3days (X=Cl). Upon exposure to visible light these complexes isomerize to the respective trans-dicarbonyl complexes within a few hours. The visible-light reaction seems to involve reversible CO dissociation. The isomerization can be repeated serval times. A mechanistic rationale for this isomerization process is established by means of DFT calculations.

Enhancement of photocatalytic activity of TiO2 by plasma irradiation

In this study, plasma irradiations to titanium were conducted to enhance the photocatalytic activity of titanium oxide. When titanium is exposed to He plasmas, various morphology changes occur as forming nano-bubbles near the surface. Photocatalytic activity of the oxidized helium plasma irradiated titanium samples with nano-cones and microstructures were assessed by the hydrogen production from aqueous methanol solution. It is shown that the He plasma irradiation increases the photocatalytic activity more than double. Moreover, nitrogen mixture plasma irradiation to titanium (oxide) was conducted for doping nitrogen, which has been regarded as method to create visible light reactivity. It is shown from X-ray photoelectron spectroscopy (XPS) analysis that nitrogen doping has been successfully conducted under specific conditions.

TiS2 transformation into S-doped and N-doped TiO2 with visible-light catalytic activity

S-doped rutile has been prepared for the first time by hydrothermal reaction of TiS2 in hydrochloric acid at a low temperature (180°C), with the S atoms in three states of TiSTi, TiSO and SO4. TiS2 in nitric acid can also be transformed into TiO2, but with mixed phases of anatase and rutile, containing nitrogen atoms at interstitial sites in the form of TiON or TiNO. The STiO2 catalyst shows a better visible-light reactivity toward adsorbed methylene blue (MB) photodegradation and hydroxylation of terephthalic acid with respect to the NTiO2. The possible reasons leading to the high photoactivity of the STiO2 are discussed in terms of the incorporated sulfur states.

Electronics, Vacancies, Optical Properties, and Band Engineering of Red Photocatalyst SrNbO3: A Computational Investigation

SrNbO3, a newly developed red photocatalyst for water splitting, has shown excellent visible light reactivity. The present first-principle calculations show that the red color of SrNbO3 is essentially resulted from Sr-vacancies, which can effectively narrow the energy gap between fully occupied bands (B–1) and partially empty conduction bands (CB). In addition to vacancy defects, doping by potassium or nitrogen has been explored to be another strategy to narrow the B–1–CB gap.

Regeneration effect of visible light‐curing furfuryl alginate compound by release of epidermal growth factor for wound healing application

ABSTRACTA visible light‐curable polysaccharide conjugate was prepared and was included with epidermal growth factor (EGF) for wound healing application. Alginate was modified with furfurylamine, and the furfuryl alginate (F‐alginate) was mixed with Rose Bengal for visible light reactivity. The introduction of furfuryl group was confirmed by 1H‐NMR and UV/vis spectroscopy. Visible light‐induced crosslinking was evaluated by micropatterning and weight measurement. Swelling ratio was also determined. To verify its applicability in wound healing applications, EGF was included in the system of F‐alginate and Rose Bengal. After the confirmation of no cytotoxicity of F‐alginate and murine EGF release from the system, cell proliferation, antibacterial activity, and animal test were performed on the system. In conclusion, it was demonstrated that the system was useful for wound healing. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40113.

Visible light photoreactivity from hybridization states between carbon nitride bandgap states and valence states in Nb and Ti oxides

For better efficiency as photocatalysts, N-doping for visible light reactivity has been intensively studied in Lamellar niobic and titanic solid acids (HNb3O8, H2Ti4O9), and its microscopic structures have been debated in this decade. We calculate the layered solid acids’ structures and bandgaps. Bandgap reduction by carbon nitride adsorption in interlayer space is observed computationally. It originates from localized nitrogen states which form delocalized top-valence states by hybridizing with the host oxygen states and can contribute to photo-current.

The Morphology Effect on Ca-Bi-O System Photocatalytic Property under Visible-Light Irradiation

Four main phases in Ca-Bi-O systems, Ca6Bi6O15, Ca4Bi6O13, CaBi2O4 and Ca5Bi14O26 were prepared by solid-state reaction method. UV-visible absorption spectra show that the samples of CaBi2O4, Ca4Bi6O13 and Ca5Bi14O26 have visible-light reactivity with the band gap of 3.08 eV, 2.76 eV and 2.60eV, respectively. The results of SEM and BET measurements indicate that CaBi2O4 has the morphology of flower-like nanostructure and the high BET surface area, while Ca6Bi6O15, Ca4Bi6O13, and Ca5Bi14O26 have the morphology of particles of various shapes with a diameter from 200 nm to 2 μm and low BET surface area. CaBi2O4 was found to be a most efficient visible-light-driven photocatalyst in degradation MB. This work may deepen the understanding of the relationship between the photocatalytic properties and the crystal structures in Ca-Bi-O system.