Strong Visible Light Absorption Research Articles

DhaTph Tubes and DhaTph‐Cu Tubes with Hollow Tubular Structure and Their Photocatalytic Reduction of CO2

AbstractPorphyrinic covalent organic frameworks (COFs, specifically DhaTph) in the absence or presence of Cu2+in porphyrin centers, were synthesized by a Schiff base condensation reaction of 5,10,15,20‐tetrakis(4‐aminophenyl)‐porphyrin (Tph) and 2,5‐dihydroxyterephthalaldehyde (Dha). Using 2,4,6‐trimethylbenzaldehyde (TBA) as a competition reagent, the hollow DhaTph Tubes and DhaTph‐Cu Tubes were obtained under solvothermal conditions. A detailed mechanism of formation of the tubular microstructure revealed the time‐dependent transformation into the tube via migration of the unstable central part of the initial solid rod. The DhaTph‐Cu Tubes possessed a high photoreduction efficiency of CO2and the rate constants of CO and methane production are 15.9 and 13.7 μmol g−1 h−1in the absence of any cocatalysts, which is about 3 and 7.6 times of DhaTph COF, respectively. The high effective photocatalytic reduction of CO2activity of DhaTph‐Cu Tubes is attributed to the high specific surface area, strong absorption of visible light, and the fast separation and transferability of electrons and holes. This work not only provides in‐depth insights into the formation mechanism of the tubular COF but also reveals the relation between the morphology and the photocatalytic property based on COFs.

Visible light-induced Silver and Lanthanum co-doped BiVO4 nanoparticles for photocatalytic dye degradation of organic pollutants

• Ag and La-doped BiVO 4 have been synthesized by a simple hydrothermal route. • The photocatalytic activity of samples was examined using XyO and Rh-B. • The doped materials showed enhanced degradation efficiency. The photocatalytic degradation of Xylenol orange (XyO) and Rhodamine B (Rh-B) is investigated in this study using the heterogeneous photocatalytic method. Silver (Ag) and Lanthanum (La) co-doped BiVO 4 photocatalysts have been synthesized using hydrothermal methods. In this study, the effect of Ag and La doping on the crystal structure, morphology and photocatalytic properties of the BiVO 4 nanoparticles have been investigated. The synthesized photocatalysts have a monoclinic scheelite structure. The pinecone-shaped Ag/La-BiVO 4 particles have shown an increased photocatalytic activity, which is thought to be due to its narrow bandgap energy, porous structure and strong visible light absorption. The photoluminescence intensity of the doped BiVO 4 has decreased significantly when compared to pure BiVO 4 due to the quenching of photoemission in the presence of Ag and La, which improves the efficiency of photocatalytic dye degradation. The time-resolved PL decay obeyed a triexponential pattern with a maximum lifetime of 90.95 ns. The doped materials showed enhanced degradation efficiency of 93% and 95% for XyO and Rh-B followed by a pseudo-first-order rate constant of 0.014 min −1 . This study will benefit in the rapid and low-cost preparation of Ag/La-BiVO 4 for photocatalytic degradation of water pollutants.

Ag-induced anatase-rutile TiO2−x heterojunction facilitating the photogenerated carrier separation in visible-light irradiation

Nanocomposites Ag-TiO2−x have been fabricated simply by Ag+ ion exchange of H2Ti3O7 nanowires. Ag NPs, appearing on the catalyst surface, exhibit strong visible-light absorption and generate hot electrons due to their localized surface plasmon resonance. Moreover, Ag introduction leads to the generation of anatase-rutile biphase heterojunction with Ti3+ defect energy level, narrowing the bandgap to 2.85 eV and inhibiting the recombination of electron-hole pairs, thus facilitating photocatalytic reduction of Cr (VI) under visible light. A possible photocatalytic reduction mechanism, i. e., the synergistic effect of the Ti3+ defect energy level, anatase-rutile heterojunction and SPR effect of Ag nanoparticles, has also been proposed.

Metal-cation-mixed lead-less two-dimensional hybrid perovskites with high carrier mobility and promoted light adsorption

The metal cation mixing in hybrid perovskite has been suggested as an effective strategy not only to promote the performance and stability but also to reduce the content of toxic lead element for environmental and health concerns. However, such a strategy has yet been well demonstrated in two-dimensional (2D) hybrid perovskites with multilayered thickness (n > 1). Here, we theoretically investigated the lead-less and lead-free 2D hybrid perovskites with tin-lead (Sn–Pb) and germanium-tin (Ge–Sn) mixed metal cations, namely, the BA2MAn-1Snn/2Pbn/2I3n+1 and BA2MAn-1Gen/2Snn/2I3n+1 (BA: C4H9NH3+; n = 1–4), by means of first-principle calculations. It is found that the electronic structure and light absorption properties of the 2D hybrid perovskites can be efficiently tuned to the optimal range for solar cells by combining the metal cations mixing and the layer thickness (n) adjustment. Markedly, due to the enhanced in-plane elastic modulus but greatly reduced deformation potential constant, both the Ge–Sn and Sn–Pb mixed 2D perovskites show high carrier mobility (∼103−104 cm2V–1S−1), which are superior to that of their 3D analogues. Moreover, the Sn–Pb mixed 2D perovskites expose much stronger visible light absorption than the non-mixed Sn- or Pb-based 2D perovskites. In addition, the in-air stability of metal-cation-mixed 2D hybrid perovskites are greatly improved compared to the 3D halide perovskites. This work suggests the great potential of the metal-cation-mixed 2D hybrid perovskite for photovoltaic and optoelectronic applications with largely reduced lead content.

Bandgap-engineered ferroelectric single-crystalline NBT-BT based nanocomposites with excellent visible light-ultrasound catalytic performance

Bandgap engineered ferroelectrics exhibit encouraging multi-energy catalytic performance by coupling the piezoelectricity and photoexcitation, which shows immense potential for environmental remediation and fuel production. However, it is challenging to prepare nano single-crystalline ferroelectric piezo-photoelectric with strong visible light absorption ability. Here, Ni mediated NBT-BT(NBT-BNT) single-crystalline nanocubes around 100 nm with considerable visible light absorption were synthesized by a high-temperature hydrothermal method. The mechanism of Ni2+ on the formation of NBT-BT nanocubes was proposed. The catalytic efficiency of NBT-BNT nanocubes is enhanced by decorating carbon quantum dots (CQDs). The RhB can be degraded within 8 min and the hydrogen production rate reaches up to ∼350 μmol g-1h-1 under visible light-ultrasonic condition. Moreover, under the simulated sunlight-ultrasound condition, RhB can be degraded within merely 3 min and a high H2 production rate of ∼747 μmol g-1h-1 is achieved. This work presents a paradigm for preparing ferroelectric single-crystalline nanocatalysts for multi-energy catalytic application.

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.

Facile development of carbon quantum dot deposited titanate-based materials for environmental application

In this study, we reported a facile EDTA-Na2 assisted method to synthesize CQD deposited titanate based materials for photocatalytic degradation of methylene blue (MB) dye. A variety of characterization methods (XRD, FTIR, DRS, Raman, UV–Vis, BET, etc.) were used to study the characteristics of the obtained materials. The results showed that the CQD deposited titanate based materials had stronger visible light absorption than the pristine titanate-based materials. Moreover, they also exhibited the enhanced photocatalytic activity in the degradation of MB into CO2. More than 90% of MB was quickly removed by one of these materials after 90-min reaction which obeyed the first-order kinetic model. .OH, .O2− and h+ were dominant active species for the MB photodegradation.

Bi@H-TiO2/B-C3N4 heterostructure for enhanced photocatalytic hydrogen generation activity under visible light

Herein, a ternary Bi@H-TiO2/B-C3N4 type II heterostructure is successfully designed and prepared via metal Bi as cocatalyst for photocatalytic H2 generation. As expected, under λ > 300 nm light, the highest photocatalytic hydrogen production rate (HPR) of Bi@H-TiO2/B-C3N4 is up to 223.08 μmol g−1 h−1. Excitingly, under visible light (λ > 400 nm), the highest HPR of Bi@H-TiO2/B-C3N4 is increased to 18.84 μmol g−1 h−1, which is about 67.3 times, 37.7 times and 6.8 times as high as that of H-TiO2, B-C3N4 and H-TiO2/B-C3N4 under the same conditions, respectively. Moreover, the electrochemical impedance spectroscopy and transient photocurrent tests manifest that the interface resistance of Bi@H-TiO2/B-C3N4 composite decreases and the photocurrent density increases after loading metal Bi. These results indicate that loading metal Bi as cocatalyst (providing more electron trapping sites) is beneficial to improve photocatalytic activity in the type II heterostructure composite. And the electron transfer directions (B-C3N4 → H-TiO2 → Bi or B-C3N4 → Bi) are proved by ultraviolet photoelectron spectroscopy test. Therefore, the Bi@H-TiO2/B-C3N4 photocatalyst with strong visible light absorption is expected to be a promising candidate in photocatalytic fields under visible light.

Insight into the Growth Mechanism of Mixed Phase CZTS and the Photocatalytic Performance.

In this work, CZTS particles with a mixed phase of wurtzite and kesterite were synthesized by the solvothermal method. The time-dependent XRD patterns, Raman spectra, SEM, and EDS analysis were employed to study the growth mechanism of CZTS. The results revealed that the formation of CZTS started from the nucleation of monoclinic Cu7S4 seeds, followed by the successive incorporation of Zn2+ and Sn4+ ions. Additionally, the diffusion of Zn2+ into Cu7S4 crystal lattice is much faster than that of Sn4+. With increasing time, CZTS undergoes a phase transformation from metastable wurtzite to steady kesterite. The morphology of CZTS tends to change from spherical-like to flower-like architecture. The mixed-phase CZTS with a bandgap of 1.5 eV exhibited strong visible light absorption, good capability for photoelectric conversion, and suitable band alignment, which makes it capable to produce H2 production and degrade RhB under simulated solar illumination.

Photothermal oxidation of cyclohexane over CoLaOx/WO3 Z-scheme composites with p-n heterojunction in solvent-free conditions

Photothermal oxidation of cyclohexane with molecular oxygen in solvent-free is considered to be an efficient approach for the formation of cyclohexanone and cyclohexanol (KA oil), and possesses the potential to generate the next stage product of adipic acid (AA) by one-pot oxidation in chemical industry. Herein, a unique type of Co8La1Ox/WO3 Z-scheme nanocomposites with p-n heterojunction was successfully constructed by a facile process of solvothermal reaction in conjunction with the simple impregnation method. The Co8La1Ox/WO3 Z-scheme heterojunction nanocomposites achieved an excellent catalytic performance for the photothermal oxidation of cyclohexane at 120 ℃ under visible light in solvent-free conditions. Surprisingly, 10.35% conversion of cyclohexane with 98.75% selectivity of KA oil (liquid, 80.97%) and AA (solid, 17.78%) was achieved during the reaction time of 3 h. Moreover, the desirable durability and stability of the Co8La1Ox/WO3 composites demonstrated a potential application as an industrial catalyst. The outstanding catalytic performance of the Co8La1Ox/WO3 composites could be ascribed to the enhanced electron excitation capacity, the accelerated electron-hole separation and migration, the inhibited charge recombination, the strong visible-light absorption, and the efficient synergetic catalytic effect of photo-thermo. Besides, high oxygen adsorption capacity and large specific surface area of the Co8La1Ox/WO3 composites can efficiently build a bridge between cyclohexane and O2 to fully utilize the oxygen participation in the oxidation. The present approach provides a promising perspective for the designing and constructing of Z-scheme heterojunction catalyst with a high-efficiency photo-thermo catalytic performance in the oxidation of cyclohexane to KA oil and AA in chemical industry.

Photocatalytic applications of 2D surface decorated boron phosphides: A density functional theory investigation

Designing high efficiency water splitting photocatalysts remains a great challenge. Base on density functional theory calculations, novel 2D functionalized hexagonal boron phosphides breaking mirror symmetry are demonstrated as free-standing stable nanoflakes. It is systematically demonstrated that bilayer HPBCl and BrPBCl are potential water splitting photocatalysts, due to their moderate band gap, spatial separation of photoexcited carriers, adequate external potential for water redox reactions, and strong visible light absorption. For traditional photocatalysts, the water splitting redox potential demands a band gap limit of EG > 1.23 eV, causing a great waste of infrared light accounting for nearly fifty percentage of the solar energy. Interestingly, bilayer HPBBr, with a small band gap of 0.43 eV, can not only show excellent energy harvest on infrared light as well as on visible light, but also simultaneously provide suitable redox potentials by adjusting pH value.

Fe-doped WO3 nanoplates with excellent bifunctional performances: Gas sensing and visible light photocatalytic degradation

A series of Fe-doped WO3 nanoplates with various Fe contents (0.5%−5%) were prepared successfully by a facile hydrothermal method. The samples were characterized and their gas sensing and visible light photodegradation properties were investigated systematically. The corresponding reaction mechanisms were proposed based on the experimental results. The results show that the Fe-doped WO3 nanoplates exhibit enhanced gas sensing to acetone and visible light photodegradation to methyl blue (MB). Particularly, the gas sensing response value of the 2 %Fe-WO3 sensor is 2.8 times higher than that of the undoped WO3 sensor. Over a low dosage (10 mg) of the 0.5 %Fe-WO3 catalyst, the photocatalytic degradation rate of the 30 mg L-1 of MB solution reaches as high as 96.8% within a short time (60 min), which is 16.8% higher than that of the undoped WO3. The Fe doping significantly accelerates charge transfer rate of the sample, resulting in the remarkable enhancement in gas sensing response. The excellent photocatalytic activity of the 0.5 %Fe-WO3 may be attributed to the improved charge transfer/separation, the stronger visible light absorption and the lower band-edge potentials. Besides the main active species O2−⋅, ·OH (the secondary active species) also contributes to photodegradation of MB.

Loading Nano-CuO on TiO2 Nanomeshes towards Efficient Photodegradation of Methylene Blue

In order to improve the photocatalytic activity of TiO2, we successfully loaded nano-CuO on the TiO2 nanomeshes as CuO-TiO2 nanocomposites through a facile electrodeposition method. The optimized calcined temperature after Cu electrodeposition is confirmed as 450 °C, which could furthest assist the crystallization of anatase TiO2 and guarantee the high photocatalytic activity of CuO-TiO2 nanocomposites. Comparing with pure TiO2 nanomeshes, CuO-TiO2 nanocomposites showed better degradability of methylene blue, and the degradation efficiency reached to 35% after 120 min irradiation. Additionally, CuO-TiO2 nanocomposites exhibit much stronger absorption intensity within the visible light scope, more than two times than that of pure TiO2 nanomeshes, which indicates that the loading of nano-CuO could promote photocatalytic efficiency by the strong visible light absorption. Additionally, CuO-TiO2 nanocomposites show faster photocurrent response and lower charge transfer resistance than that of pure TiO2 nanomeshes, which implies that the recombination rate of photogenerated electron-hole pairs was reduced after nano-CuO loading.

A Polyimide-Based Photocatalyst for Continuous Hydrogen Peroxide Production Using Air and Water under Solar Light

A Polyimide-Based Photocatalyst for Continuous Hydrogen Peroxide Production Using Air and Water under Solar Light

Ternary TiO2@Bi2O3@TiO2 hollow photocatalyst drives robust visible-light photocatalytic performance and excellent recyclability

The development of visible-light photocatalysts with excellent catalytic activity and recyclability still remains a big challenge. Here, we present a facile template and self-assemble strategy to design new confined ternary photocatalyst by embedding Bi2O3 (p-type) into hierarchical hollow TiO2 (n-type) spheres (TiO2@Bi2O3@TiO2). The obtained TiO2@Bi2O3@TiO2 photocatalyst exhibits strong visible-light absorption and efficient charge separation due to its unique n-p-n heterojunction, effectively driving the complete degradation (100%) of tetracycline according to the characteristic peak (∼350 nm) and TOC results of TC under visible light (λ > 420 nm). Interestingly, the introduction of confinement effect considerably promotes cyclic stability, especially in a strong acid (pH=3.0) or alkali (pH=11) environment. Moreover, the photodegradation intermediates and pathways are demonstrated by LC-MS measurement. This finding provides a new idea to design other confined photocatalysts with a ternary heterojunction for clean energy and environment applications.

Mechanism research of catalytic degradation of 1, 2-dichlorobenzene over highly efficient hollow calcium ferrite by in situ FTIR spectra

The hierarchical CaFe2O4 core-shell hollow microspheres are successfully fabricated by a facile solvothermal approach following heat treatment process. The hollow architecture exhibits high surface area and strong visible-light absorption capability. Meanwhile, the formation mechanism of hollow structure is proposed based on characterization results. Furthermore, the photocatalytic activity is tested by 1, 2-dichlorobenzene degradation under visible light irradiation, and the degradation ratio of CaFe2O4 core-shell hollow microspheres can reach 82.0% after 8 h. Moreover, relying on the in situ Fourier transform infrared technology, the catalytic oxidation process and degradation mechanism is clarified on CaFe2O4 surface, and the intermediate product (formate, acetate, maleate species, etc.) and the mineralized products (CO2 and H2O) are identified finally.

A facility synthesis of bismuth-iron bimetal MOF composite silver vanadate applied to visible light photocatalysis

The metal-organic framework (MOF)-based photocatalytic technology has received widespread attention due to its excellent properties (such as adjustable aperture structure and unique optical response). A facile sheet-like sliver vanadate/Bi–Fe MOF (AGV/HBF) heterojunction composite is successfully synthesized by introducing in situ precipitation AgVO3/Ag4V2O7 (AGV) nano-particles on the interface of Bi–Fe MOF. Herein, HBF is used as a template, and the morphology of the layer cake provides a suitable environment for the growth of nano-silver vanadate particles. The composite photocatalyst is characterized using XRD, FTIR, SEM, EDS, and XPS. HBF and AGV/0.25HBF worked well in the photocatalytic decomposition of rhodamine B (RhB) under visible light. The degradation efficiency reached 77.1% and 99.4% under visible light irradiation for 2 h, separately. The enhanced photocatalytic performance of the AGV/0.25HBF nanocomposite can be attributed to the strong visible-light absorption, unique nanostructures, and low recombination of electron-hole pairs due to the as-formed heterojunctions. In addition, the stability and photoelectric properties of HBF and AGV/0.25HBF are also discussed. Hope these studies can assist with the research and wide application of MOF-based photocatalysts.

Controlling the charge carriers recombination kinetics on the g-C3N4-BiSI n-n heterojunction with efficient photocatalytic activity in N2 fixation and degradation of MB and phenol

The challenges like the photocatalytic reduction of N2 and elimination of contaminants from the wastewater are accessible by low cost, stable, and visible-light-driven semiconductor-based photocatalysis. A novel g-C3N4/BiSI nanocomposite was synthesized by hydrothermal method and applied for the first time in photocatalytic nitrogen fixation and degradation of methylene blue dye and phenol. The physicochemical features of the photocatalysts were studied by XRD, XPS, FTIR, BET, DRS, FESEM, TEM, EDX mapping, PL, EIS, Mott-Schottky, and photocurrent techniques. Experimental results showed that the production of ammonia in the presence of g-C3N4/BiSI nanocomposite was 1280 μmolL−1g−1, while this values for g-C3N4 and BiSI were 274 μmol g−1 L−1 and 126 μmol g−1 L−1, respectively. Moreover prepared nanocomposite exhibited a higher rate constant in the MB (537.5 × 10−4 min−1) and phenol (353 × 10−4 min−1) degradation compared with the counterparts. The charge separation efficiency obviously improved, which was ascribed to the charges migration between g-C3N4 and BiSI in an n-n heterojunction system. In addition, high specific surface area and strong visible light absorption were identified as other factors affecting photocatalytic performance. This unique heterojunction photocatalyst has wide application prospects in environmental treatment.

Synthesis of β-Bi2O3 nanoparticles via the oxidation of Bi nanoparticles: Size, shape and polymorph control, anisotropic thermal expansion, and visible-light photocatalytic activity

Bismuth trioxide (Bi2O3) is known for its simple composition but rich polymorphism that allows a number of phase-dependent physicochemical properties and technical applications. We here report our controllable synthesis of highly discrete β-Bi2O3 (tetragonal) nanoparticles (NPs) via the thermal oxidation of nearly-monodisperse Bi NPs. The size and shape (spherical and tear- or rod-like) of β-Bi2O3 NPs are tunable by the size of parent Bi NPs whereas β and α (monoclinic) polymorphs can be selectively achieved by tailoring the oxidation temperature. The phase stability of β polymorph from room temperature to 450 °C enables us to perform an in situ high-temperature XRD study on the temperature dependence of its lattice parameters, which reveals a marked thermal expansion anisotropy in β-Bi2O3 with a linear thermal expansion coefficient of +35.1 × 10−6 °C−1 in the c axis, fifteen times higher than that in the a axis. Meanwhile, the narrow band gap (2.27 eV for β vs. 2.77 eV for α) and strong visible-light absorption endow β-Bi2O3 NPs with a good photocatalytic activity for the visible-light Rhodamine B dye degradation. We expect that our work could be a valuable reference for the studies on the size, shape and polymorph control, thermal property, and photocatalytic application of Bi2O3.

Metal-Organic-Framework-Derived Ball-Flower-like Porous Co3O4/Fe2O3 Heterostructure with Enhanced Visible-Light-Driven Photocatalytic Activity.

A porous ball-flower-like Co3O4/Fe2O3 heterostructural photocatalyst was synthesized via a facile metal–organic-framework-templated method, and showed an excellent degradation performance in the model molecule rhodamine B under visible light irradiation. This enhanced photocatalytic activity can be attributed to abundant photo-generated holes and hydroxyl radicals, and the combined effects involving a porous structure, strong visible-light absorption, and improved interfacial charge separation. It is notable that the ecotoxicity of the treated reaction solution was also evaluated, confirming that an as-synthesized Co3O4/Fe2O3 catalyst could afford the sunlight-driven long-term recyclable degradation of dye-contaminated wastewater into non-toxic and colorless wastewater.