Visible Light Absorption Capacity Research Articles

Visible light assisted heterojunction composite of AgI and CDs doped ZIF-8 metal-organic framework for photocatalytic degradation of organic dye

• CDs@ZIF-8@AgI was prepared by a solvent-free way coupled to ion deposition strategy. • Acridine Orange can be effectively degraded by CDs@ZIF-8@AgI under visible light. Water pollution induced by the productive process of organic dyes would lead to various diseases, and so treatment of the wastewater is an urgent task for protecting human health and ecological environment. In this work, visible light responsive heterojunction material based on silver iodide and carbon dots (CDs) doped ZIF-8 metal organic frameworks (CDs@ZIF-8@AgI) has been prepared by a green solvent-free strategy and in-situ ion deposition method. The CDs@ZIF-8@AgI composites have high photocatalytic performance for degradation of acridine orange (AO) dye under visible light, and the maximum degradation percentage can reach to 96.0%, which was estimated by the UV-visible spectroscopy. The porous structure and large surface area of the photocatalyst were favorable to absorption of the target dye on the catalyst, which can promote the kinetic degradation rate for low level concentration of the dye. The introduction of CDs into the AgI heterojunction can improve the electron transport efficiency and visible light absorption capacity, and thus significantly enhancing the photocatalytic activity of the catalyst. The photocatalytic mechanism was proposed as indirect Z-scheme heterojunction type based on the energy band structure of the catalyst. This work provides a visible light photocatalyst for removal of the AO dye in wastewater and offers a promising strategy for developing photocatalyst for treatment of organic pollutants in the environment using solar energy.

The tunable electronic structure and optical properties of vacancy-ordered double perovskites Tl2PdBrxCl6-x (x = 0, 2, 4, 6)

Double perovskites show excellent stability and suitable band gaps, which are superior materials for solar cell applications. In this work, the structure, electronic, and optical properties of vacancy-ordered double perovskites Tl2PdBrxCl6-x (x = 0, 2, 4, 6) are explored by first-principles calculations. The tunable band gaps of the studied compounds are in the range of 1.3–2.2 eV. The band gap is narrowed from Tl2PdCl6 to Tl2PdBr6. Moreover, the band gap of Tl2PdCl6 can be adjusted to the appropriate band gap value through minor Br doping. High concentration of Br doping results in a small band gap variation. The visible light absorption capacity is significantly enhanced from Tl2PdCl6 to Tl2PdBr6. The results show that three compounds including Tl2PdBr2Cl4, Tl2PdBr4Cl2, and Tl2PdBr6 are promising materials for potential optoelectronic applications.

High selective conversion of fructose to lactic acid by photocatalytic reforming of BiOBr/Znx@SnO2-n in alkaline condition

Herein, a novel p-n type BiOBr/Znx@SnO2-n photocatalyst was designed by using BiOBr coupling with large specific surface area Zn doped SnO2 through a facile in situ approach. The composite possesses proper redox potential as well as high efficiency interfacial charge transfer capability. Coupling BiOBr with Zn doped SnO2 is proved efficiency to form a facile bandgap regulation mechanism and could adjust the absorption capacity of visible light, thus enhances the photocatalytic performance effectively. The photocatalyst exhibits high efficiency in photo-reforming of fructose to lactic acid under alkaline conditions, achieving a maximum yield of 79.6% and still achieving a lactic acid yield of 70.7% even after five cycles of recycling. Possible pathways of the lactic acid production were proposed based on the generation of active oxidative radicals and the products detected during the reaction. Therefore, this work provides an effective approach for biomass conversion through rational photocatalyst design.

Enhanced photocatalytic water splitting of g-C3N4 loaded with Fe doped Co3O4 and Pt dual-cocatalysts

Dual cocatalysts play an important role in photocatalytic water splitting to hydrogen production. In this paper, Fe-doped Co3O4 (Fe-Co3O4) and Pt were loaded on the surface of g-C3N4 to enhance the water photocatalytic splitting, in which Fe-Co3O4 was used as an oxidation cocatalyst to capture the photo-generated holes of g-C3N4, and Pt was used as a reduction cocatalyst to transfer photo-generated electrons. Under the irradiation of visible light, its hydrogen production rate reaches up to 3.015 mmol g−1 h−1, which is 3.01 times higher than that of g-C3N4 loaded with Pt. Pt and Fe-Co3O4 dual cocatalysts not only promote the migration rate of photo-generated electrons and holes on the surface of g-C3N4, but also improve the light absorption capacity of visible light. The interfacial electric field built from the p-n heterojunction of Fe-Co3O4/g-C3N4 drives photo-generated electrons in Fe-Co3O4 flowing to the holes of g-C3N4, which further inhibiting the recombination of g-C3N4 photo-generated carriers. This work provides a reference for the development of high-efficiency photocatalyst and an effective support for the development of semiconductor cocatalyst.

Mechanochemical construction of Bi1-xLaxOI solid solution with abundant oxygen vacancies for enhanced photocatalytic oxidation of inorganic/organic arsenic

Bismuth oxyiodide is one of the bismuth-based semiconductors which exhibits narrow band gaps and excellent visible light response, however modification strategies are usually desired for improving its photocatalytic reactivity. In this context, introduction of valuable components into the interlayer of BiOI is expected to work, considering its typical layered structure. In this case, mechanochemical synthesis of BiOI, with simultaneous introduction of lanthanum into its interlayer to form Bi1-xLaxOI, was conducted for the first time, and arsenic (As(III)) was selected to evaluate the photocatalytic reactivity, demonstrating excellent reaction efficiency for arsenic oxidation under a mild condition. Characterizations confirmed the incorporation of La and the presented well crystalline structure of Bi1-xLaxOI, and revealed its better visible light absorption capacity than raw BiOI. Besides the excellent electronic conductivity of Bi0.9La0.1OI, photogenerated holes (h+) and superoxide radical species (·O2-) were characterized by electron spin resonance (ESR) test, to act as predominant reactive groups during the photo-induced oxidation reaction. These findings provided a novel concept for the interlayer decoration of BiOI, and offered an alternative approach to develop its potential application for the removal of hazardous arsenic pollutants.

Au nanoparticles-modified S-scheme In2O3/H1.5CN heterojunction with enhanced photocatalytic CO2 reduction activity

The construction of S-scheme heterojunction is of great significance for the photocatalytic reduction of CO2. Here, we prepared two-dimensional (2D) ultra-thin g-C3N4 by acidifying the carbon nitride precursor, and used In2O3 to construct a S-scheme heterojunction with 2D g-C3N4, and finally In2O3/H1.5CN was modified with Au nanoparticles. The physicochemical properties of the prepared materials were studied by SEM/TEM, XPS, DRS, PL and photochemical test. Meantime, the S-scheme charge transfer mechanism was demonstrated by UPS and ESR. As a result, on the one hand, S-scheme heterojunction accelerated the transfer of electrons on the CB of In2O3 to the VB of g-C3N4, avoided the recombination of photon-generated carrier. On the other hand, Au, as an effective cocatalyst, promoted photoinduced electron transfer and provided more active sites for CO2 reduction and the local surface plasmon resonance phenomenon caused by Au NPs enhanced the visible light absorption capacity of the composite material. Moreover, 2D thin layer of g-C3N4 played a carrier effect to disperse In2O3 cube. Therefore, In2O3/H1.5CN/2Au had stable CO2 reduction products, and the yields of CO/CH4 reached 141.24/77.05 μmol/g.

Polyaniline enwrapped CoFe2O4/g-CN ternary nanocomposite for adsorption driven photocatalytic degradation of explicitly diverse organic pollutants

The present study strives to unlock the potential of CoFe2O4 supported over graphitic carbon nitride (g-CN) and polyaniline (PANI) as photocatalyst for wastewater decontamination. For this purpose, a series of PANI@CoFe2O4/g-CN (PA-CNC) nanocomposites were fabricated by varying PANI: CoFe2O4/g-CN ratio (0.25:1, 0.5:1, 1:1 and 2:1) employing in-situ oxidative polymerization method. The structure, morphology, optical and magnetic properties of the nanocomposites were characterized using FT-IR, Raman, XRD, FE-SEM, HR-TEM, XPS, UV-DRS, PL, EIS, VSM and BET analysis. The ternary nanocomposites were investigated for the removal of ofloxacin (OFX), sulfamethoxazole (SFX), p-nitrophenol (PNP) and malathion (MT) as model pollutants. Under optimized reaction conditions, the pseudo-first order rate constant value of PA-CNC (0.5:1) nanocomposite for the degradation of OFX (5.3 × 10−2 min−1) was observed to be nearly 4 times to that of pristine CoFe2O4 (1.3 × 10−2 min−1). The incorporation of PANI has improved the adsorption capacity of nanocomposites owing to synergistic effect of different interactions between pollutant molecules and PANI that subsequently augmented the rate of photocatalytic degradation of pollutants. Moreover, PANI improved the visible light absorption capacity and promoted the separation of photogenerated charge carriers across the ternary heterojunction. The magnetic recyclability up to four cycles highlighted the desirability of PANI@CoFe2O4/g-CN nanocomposites for the abatement of wide range of pollutants.

Synergy of nitrogen vacancies and nanodiamond decoration in g-C3N4 for boosting CO2 photoreduction

Photoconversion of CO2 into fuel is critical for realizing a net-zero emission future, but it remains an open challenge due to the unsatisfactory light absorption and photogenerated carriers’ separation efficiency of catalysts. In this work, upon in situ thermal polymerization method, the nanodiamond (ND) are homogeneously and solidly modified on the defective graphitic carbon nitride (g-C3N4) surface. Under visible light irradiation, the ND/g-C3N4(NH) exhibits excellent CO2 photocatalytic performance with a CO yield of 10.98 μmol/h (18.6 times higher than bulk g-C3N4), predominant performance in the selectivity of CO and cyclic stability. The improved CO2 photoreduction ability was sourced from the synergetic effect of nitrogen vacancies engineering and ND decoration, which also significantly improved visible light absorption capacity and facilitated electron transport pathways, and promoted the separation and transfer of charge carriers efficiently.

Surface engineering of hematite nanorods photoanode towards optimized photoelectrochemical water splitting

Rapid charge recombination in hematite (Fe2O3) during photoelectrochemical water splitting is a major obstacle to achieving high-efficiency photoelectrodes. Surface defect engineering is considered as a viable strategy for enhancing photoelectrochemical activity of oxide photoanodes. Herein, a one-dimensional (1D) defective γ-Fe2O3 nanorods (DFNRs) photoanode is prepared using solvothermal and high-temperature hydrogenation strategies. The as-prepared DFNRs possess superior visible-light absorption capacity and exhibit excellent photoelectrochemical performance (0.98 mA cm−2), with approximately three-fold higher photocurrent density than that of pristine Fe2O3 (FNRs, 0.32 mA cm−2). The enhanced activity of the DFNRs results from the moderate formation of oxygen vacancy defects, which promotes spatial charge separation and transfer at the DFNRs/electrolyte interface, as well as the 1D nanorod structure, which favors rapid charge transfer. The surface of γ-Fe2O3 with hydroxyl (OH) groups provides sufficient surface-active sites. This result suggests that surface-oxygen deficiency of γ-Fe2O3 can not only expand the light absorption range but also facilitating photo-generated charge carriers separation. This surface engineering strategy provides an alternative method for preparing stable and highly active metal oxide photoanodes for photoelectrochemical water splitting.

Efficient visible-light-driven photoreduction of U(VI) by carbon dots modified porous g-C3N4

The efficient removal of uranium from radioactive wastewater is of great significance for the ecological environment safety and sustainable development of nuclear energy. Herein, the carbon dots modified porous graphitic carbon nitride (CNCD) was fabricated and used for photoreduction of U(VI) under visible LED light irradiation. The removal rate of U(VI) by CNCD-2 could reach more than 95 % over a wide range of U(VI) concentration. In addition, the CNCD-2 showed excellent selectivity and recyclability for photoreduction of U(VI). Further mechanism studies showed that the high photocatalysis activity of CNCD-2 was attributed to the effective separation of photoinduced electron-hole pairs, strong visible light absorption capacity and narrow bandgap. The U(VI) was activated by both photoinduced e- and •O2– in the process of photoreduction, and then immobilized by transforming it to metastudtite ((UO2)O2·2H2O). These results indicate that the CNCD is a promising material for remediation of uranium-containing wastewater under visible light irradiation.

Preparation and photocatalytic performance of UIO-66/La-MOF composite

To improve the photocatalytic degradation efficiency of photocatalytic materials UIO-66 and La-MOFs under visible-light irradiation, a series of photocatalytic materials with La and Zr as metal centers and terephthalic acid (H2BDC) and 2-amino terephthalic acid (H2ATA) as organic ligands were prepared by solvothermal method. The photocatalytic materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible (UV-vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and Mott-Schottky test. The photocatalytic degradation performance to Rhodamine B of the catalysts was fully investigated. Results show that the H2ATA series had stronger visible-light absorption capacity and better photocatalytic performance. The 0.35 La/Zr-H2ATA composite showed the best photocatalytic degradation. The quenching experiments confirmed that the active species in the photocatalytic degradation were the holes and superoxide radicals. The possible mechanisms of the carrier migration paths in the energy level matching for La/Zr-H2BDC and La/Zr-H2ATA were also discussed in detail.

Solid-Phase Synthesis of Red Fluorescent Carbon Dots for the Dual-Mode Detection of Hexavalent Chromium and Cell Imaging.

The excellent optical properties and biocompatibility of red fluorescence carbon dots (R-CDs) provide a new approach for the effective analysis of hexavalent chromium Cr(VI) in environmental and biological samples. However, the application of R-CDs is still limited by low yield and unfriendly synthesis route. In this study, we developed a new type of R-CDs based on a simple and green solid-phase preparation strategy. The synthesized R-CDs can emit bright red fluorescence with an emission wavelength of 625 nm and also have an obvious visible light absorption capacity. Furthermore, the absorption and fluorescence signals of the R-CDs aqueous solution are sensitive to Cr(VI), which is reflected in color change and fluorescence quenching. Based on that, a scanometric and fluorescent dual-mode analysis system for the rapid and accurate detection of Cr(VI) was established well within the limit of detection at 80 nM and 9.1 nM, respectively. The proposed methods also possess high specificity and were applied for the detection of Cr(VI) in real water samples. More importantly, the synthesized R-CDs with good biocompatibility were further successfully applied for visualizing intracellular Cr(VI) in Hela cells.

Incorporation of Na into Ag2ZnSnSe4 from hybrid functional calculations

In the present study, first-principles calculations are performed to study the structural, elastic, electronic, and optical properties of Ag2ZnSnSe4 (AZTSe) and Ag1.5Na0.5ZnSnSe4 (ANZTSe) for the first time. The dopant formation energy and phonon dispersion ensure the thermodynamic stability of ANZTSe. The tendency of phase separation still exists for ANZTSe. In addition, the mechanical stability of ANZTSe is confirmed. The electronic and optical properties of AZTSe and ANZTSe are analyzed by employing the hybrid functional PBE0. The results show that the substitution of Na for Ag results in the increasing band gap of AZTSe. ANZTSe is a direct bandgap compound with the value of 1.54 eV. It is found that AZTSe and ANZTSe have low carrier effective masses and show good mobility. The visible light absorption capacity of ANZTSe is slightly lower than that of AZTSe. In general, ANZTSe is the potential candidate for solar cells.

Influence of structural, electronic and optical properties of boron and nitrogen doping in tetragonal PbTiO3: insight from first-principles

The structural, electronic and optical properties of intrinsic, B- and N-doped tetragonal PbTiO3 are investigated by first-principles calculations. After doping with B (N) atom, the stability of the system decreases, but it is still thermodynamically stable. B-doped (N-doped) PbTiO3 appear new B-2p (N-2p) impurity bands near Fermi level, reducing the bandwidth from 2.02eV to 0.56eV (0.43eV). Imaginary part of dielectric function has the largest peak at the photon energy of 5.81 eV, which originates from the transition of electrons from the occupied O-2p VB states to the unoccupied Ti-3d CB states. The static refractive index of B- and N-doped PbTiO3 are larger than that of PbTiO3. B-doped (N-doped) PbTiO3 can increase the light absorption capacity of near-infrared wavelengths and visible light, and energy loss in the visible light range is very small, indicating that Band N-doping are expected to improve the optical properties of PbTiO3.

A sensitive photoelectrochemical aptasensor for enrofloxacin detection based on plasmon-sensitized bismuth-rich bismuth oxyhalide

Highly sensitive detection of enrofloxacin (ENR) is crucial for contaminant detection and environmental protection. A sensitive and selective photoelectrochemical (PEC) aptasensor was assembled by Au nanoparticles sensitized Bi24O31Br10 (Au/Bi24O31Br10) composites for detecting ENR. Due to the synergistic effect of bismuth-rich strategy and surface plasmon resonance (SPR) effect, Au/Bi24O31Br10 possessed promoted visible light absorption capacity further enhancing PEC performance and detection sensitivity of the constructed PEC aptasensor. By chemically adsorption effect between the sulfhydryl modified aptamer and Au nanoparticles, the ENR-aptamer was introduced into the PEC sensor to achieve highly selective detection of ENR. The PEC ENR aptasensor based on Au/Bi24O31Br10 composites possessed a broad linear detection scope (0.72–36000 ng L−1), satisfactory limit of detection (0.30 ng L−1, S/N = 3), high selectivity and stability. This work provides a new way for the trace detection of antibiotics in environmental analysis field.

The composite of Zr-doped TiO2 and MOF-derived metal oxide for oxidative removal of formaldehyde at the room temperature

Formaldehyde (HCHO) is a common organic pollutant, and it is necessary to prepare an efficient catalyst to degrade it. Metal oxides, especially TiO2, have received widespread attention in the field of HCHO degradation. In this paper, a Zr based MOF UiO-66 was added in the process of Zr doping TiO2 to enhance the ultraviolet light absorption capacity of the catalyst. Then the supported Ag by photoreduction was used to further improve the dispersibility and visible light absorption capacity of the catalyst. When 1000 mg UiO-66 is added, [email protected]–TiO2–1000U6 shows the best degradation rate of 83.4%, and has good stability. Through a series of characterizations, it was found that the ZrO2 nanoparticles derived from UiO-66 were uniformly distributed on the flake TiO2, and the visible light absorption capacity of the catalyst was significantly improved. This work provides a certain reference value for the application of MOF and its derivatives in the field of HCHO degradation.

Rational design of plasmonic Ag@CoFe2O4/g-C3N4 p-n heterojunction photocatalysts for efficient overall water splitting

Highly efficient and direct photocatalytic H2 evolution from water via water splitting without using sacrificial reagents is a challenging approach to convert solar energy into renewable and storable chemical energy. Herein, by amalgamating the architecture recommendations and energy band engineering principles into the design formulation, a novel Ag@CoFe2O4/g-C3N4 plasmonic p-n heterojunction photocatalytic system is designed and constructed for the first time. The Ag@CoFe2O4/g-C3N4 photocatalyst so designed, under the illumination of the visible-light (λ > 420 nm), produced H2 and O2 in 2:1 stoichiometric amount at the rates of 335 μmol h−1 and 186 μmol h−1, respectively, with an apparent quantum yield reaching 3.35% at 420 nm, demonstrating that Ag@CoFe2O4 dimer colloids are responsible for oxidation and g-C3N4 for reduction. Moreover, in the presence of triethanolamine, the apparent quantum yield achieved by Ag@CoFe2O4/g-C3N4 is 16.47% with hydrogen produced at the rate 3.5 times higher than the CoFe2O4/g-C3N4 heterojunction photocatalyst with AQY of 5.49%. The combination of Ag plasmonic effect and internal electric field established at the interface of p-type CoFe2O4 and n-type g-C3N4 boosts the separation efficiency of photoexcitons from CoFe2O4 to g-C3N4, extending the visible-light absorption capacity of the systems. The generation of optimum amount of defects like oxygen vacancies at the p-n heterojunction interface due to the structural distortion of CoFe2O4 also plays a prominent photocatalytic enhancement by providing active sites for the adsorption of water molecules for the light driven catalytic reactions. Our work introduces a potential avenue to design efficient photocatalysts by constructing several other suitable p-n heterojunction semiconductor photocatalysts toward practical application in solar energy conversion.

Preparation of Cu modified g-C3N4 nanorod bundles for efficiently photocatalytic CO2 reduction

Carbon nitride-based photocatalysts for CO2 reduction have received great attention. The introduction of transition metals can effectively improve the photocatalytic efficiency of carbon nitride. However, how to introduce transition metals into carbon nitride in more ways remains a challenge. Herein, the Cu modified g-C3N4 nanorod bundles (CCNBs) were prepared by chemical vapor co-deposition using the mixture of urea and chlorophyllin sodium copper salt as precursor. The prepared CCNBs exhibited excellent photocatalytic activity for CO2 reduction. The unique hierarchical structure was beneficial to enhance light harvesting. Besides, the introduction of uniformly dispersed Cu further improved the absorption capacity of visible light, increased active sites, and promoted the separation and transfer of carriers. The CO yield of CCNBs was 5 times higher than that of bulk g-C3N4, and showed excellent stability in cycle experiments. This work provides a strategy to prepare carbon nitride-based photocatalysts for efficient CO2 reduction.

Cl-based functional group modification MIL-53(Fe) as efficient photocatalysts for degradation of tetracycline hydrochloride

MIL-53(Fe) catalyst has been widely used to treat the pollutants in water. However, the limited number of electrons in MIL-53(Fe) catalyst has always affected the rate at which Fe3+ can be reduced to Fe2+. We modulated iron-based metal–organic frameworks (MOFs) using organic ligands modified with chlorine functional groups. The characterization results indicate that the 2Cl-MIL-53(Fe) catalyst exhibited the optimal photoelectric properties while maintaining the original structural characteristics. The experimental analyses and the first-principles study suggest that the introduction of a chlorine functional group not only reduced the band gap width and enhanced the visible-light absorption capacity, but also significantly enhanced the electron cloud density of Fe–O clusters. This could further accelerate the redox cycle of Fe(III)/Fe(II), beneficial for H2O2 activation. The constructed Cl-MIL-53(Fe) catalyst exhibited a 3.8 times higher reaction rate constant than pure MIL-53(Fe) catalyst. The specific TCH degradation pathway and mechanism of 2Cl-MIL-53(Fe) treatment are proposed. This study provides a new strategy for iron-based MOFs as a heterogeneous photo-Fenton catalyst to degrade pollutants in water.

Water-triggered conversion of Cs4PbBr6@TiO2 into Cs4PbBr6/CsPbBr3@TiO2 three-phase heterojunction for enhanced visible-light-driven photocatalytic degradation of organic pollutants

Poor stability and light absorption are the main factors hindering the application of Cs4PbBr6 nanocrystals (NCs) in photocatalysis, and acquiring heterostructure of semiconductor/perovskite still is a challenging task. Here, we successfully synthesized Cs4PbBr6 NCs and then coated with titania (TiO2) to construct Cs4PbBr6/CsPbBr3@TiO2 ternary heterojunction by one-pot water-triggered conversion. The newly formed interface phase of CsPbBr3 between Cs4PbBr6 NCs and TiO2 enhanced visible-light absorption capacity of composites, promoting the effective separation and transfer of photoelectron–hole pairs. CsPbBr3 interfacial phase levels in Cs4PbBr6/CsPbBr3@TiO2 can be regulated by controlling water content, and its content can affect the photocatalytic performance of the obtained composites. Ternary Cs4PbBr6/CsPbBr3@TiO2 composite exhibits highest photocatalytic activity for degradation of Rhodamine B and tetracycline in water system under visible-light irradiation, which is higher than that of CsPbBr3@TiO2 and commercial P25, respectively. Meanwhile, the obtained composite shows good stability in the water system. This work demonstrates a critical interface modulation action of CsPbBr3 for the application of Cs4PbBr6 NCs in the fields of photocatalysis.