Photocatalytic Oxidation Ability Research Articles

Ultrathin 2D[sbnd]2D WO3-x-C3N4 heterostructure-based high-efficiency photocatalyst for selective oxidation of toluene

Photocatalytic oxidation of toluene for the organic synthesis of value-added benzaldehyde has attracted great attention in recent years. However, activation of CH bonds and selective production of benzaldehyde under mild green conditions remains a great challenge. Herein, a series of two-dimensional (2D) ultrathin heterostructure-based components (WO3-x-C3N4 nanosheets), fabricated by coupling oxygen-deficient WO3-x with amorphous C3N4 via a simple electrostatic self-assembly method, was demonstrated as high-efficiency photocatalysts to produce benzaldehyde in the presence O2 as oxidant at room temperature. Under optimal conditions, the prepared 10WCN sample (10 wt% WO3-x-C3N4) exhibited improved photocatalytic oxidation ability with a good benzaldehyde selectivity (96 %) and high benzaldehyde yield (2738.6 μmol g−1 h−1) within 6 h, which is 6.6 and 3.3 times than that of pure WO3-x (412.5 μmol g−1 h−1) and C3N4 (835.7 μmol g−1 h−1). The enhanced photocatalytic performance was due to the constructed 2D type II heterojunction and abundant oxygen vacancies (OVs), contributing to the photoinduced carriers' separation and migration efficiently. This work indicates the synergistic effect of defect metal oxides and 2D ultrathin sheet-to-sheet heterojunctions in photocatalytic hydrocarbon conversion.

Molecular Engineering to Boost the Photo-Oxidase Activity of Molecular Rotors in Colorimetric Sensing of Temperatures.

Some organic dyes and photosensitizers with strong visible absorption can behave as photo-responsive oxidase mimics. However, the relationship between the photo-oxidase activity and molecular structure remains unclear to date. In this work, a new type of photosensitizer with the characteristics of molecular rotors, namely DPPy, served as the molecular scaffold for further investigation. To adjust the photocatalytic oxidation ability, DAPy and CBPy were designed and synthesized based on the enhancement and diminishment of the intramolecular charge transfer (ICT) process, respectively. Kinetic studies revealed that DAPy and CBPy both exhibited highly efficient photo-activated oxidase-like activity with 3,3',5,5'-tetramethylbenzidine (TMB) as the substrate, which were in good accordance with their molecular engineering to promote either type I or type II reactive oxygen species (ROS) generation. Impressively a colorimetric method based on the visible light induced oxidase-like activity of molecular rotors was developed to determine the environmental temperature for the first time. Both DAPy and CBPy showed distinct sensitivities toward temperature as compared with several molecular rotors based on the typical fluorimetric detection. This work provides a new strategy for the application of molecular rotors to overcome the non-emissive challenge in temperature sensing.

Uracil derivative-assisted universal synthesis of defective 2-dimensional porous flaky carbon nitride for efficient photocatalytic CO2 reduction

In this paper, three novel defective two-dimensional lamellar carbon nitride were successfully synthesized by molecular self-assembly using melamine and cyanuric acid as supramolecular aggregates and introducing three different uracil derivatives (5-formyluracil, 5-acetyluracil, uracil-5-carboxylic acid). In our previous work, we found that the introduction of thymine into supramolecular precursors has good photocatalytic oxidation ability for NO. On this basis, we discovered that by introducing uracil derivatives as ligands for supramolecular aggregates, not only two-dimensional porous sheet nanostructures can be constructed, but also abundant nitrogen and oxygen defects can be introduced, which is supported by various characterizations. These defects can effectively modulate the electronic structure of carbon nitride and thus improve the separation of photogenerated carriers. In addition, the introduction of uracil derivatives affects the energy band structure of the catalyst, and these are important factors affecting the catalytic activity. Compared with bulk carbon nitride, the synthesized materials exhibited significantly enhanced photocatalytic CO2 reduction activity under mild conditions, with CO yields of 10.34, 28.65, 32.28, and 36.48 μmol g−1h−1 for BCN, CNU2.5, CNF2.5, and CNY2.5, respectively. More importantly, with the support of in situ DRIFTS, we proposed the reaction mechanism of photocatalytic reduction of CO.

Regulation of the Tertiary N Site by Edge Activation with an Optimized Evolution Path of the Hydroxyl Radical for Photocatalytic Oxidation

Regulating the active sites to increase the yield of •OH is a specialized focus for pollutant photodegradation by g-C3N4-based photocatalysts. Herein, the tertiary N site was first tailored by edge activation to optimize the •OH evolution path. Ethyl alcohol and cyano group comodified g-C3N4 was first fabricated via a facile one-pot thermal copolymerization route to achieve a high yield of •OH. The as-prepared N20–CN exhibited first-class photocatalytic oxidation ability in the degradation of phenol (k40 min is 26.3 times higher than that of BCN). Both experimental results and DFT calculations disclose that the tertiary N site with increased electron density via synergy of the two groups realizes not only the oxygen reduction route mediated with •O2– but also the in situ conversion of H2O2 between high production and strong reduction, governing the O2 → •O2– → H2O2 → •OH optimal evolution path with a high yield of •OH. This paper provided a theoretical basis for the development of a superactive g-C3N4-based photocatalyst and optimization of •OH evolution paths via the edge activation strategy for solar-driven photochemical applications.

Fabrication of BiOIO3/g-C3N4/Er3+ containing oxygen vacancies for photocatalytic oxidation of gaseous elemental mercury

Construction of heterojunction and formation of oxygen vacancy are effective methods to improve the performance of photocatalysts. In this work, Er3+-doped BiOIO3/g-C3N4 photocatalyst with oxygen-rich vacancies was prepared by a simple hydrothermal and calcination method for the photocatalytic oxidation of elemental mercury. The structural properties of BiOIO3/g-C3N4/Er3+ were analyzed by XRD, SEM and BET. The results showed that all samples exhibited good photocatalytic oxidation ability for Hg0 under visible light irradiation. Among them, the photocatalyst with Er3+-doped BiOIO3/g-C3N4 and then calcined has the highest removal efficiency of Hg0, which is 68.83%. This may be due to the increase of oxygen vacancy caused by Er3+ doping, which enables the photocatalyst to have higher electron transfer rate and wider visible light absorption range. Finally, the possible mechanism of photocatalytic oxidation of gaseous elemental mercury with BiOIO3/g-C3N4/Er3+ photocatalyst was proposed. This study provides some reference for the design and application of photocatalysts containing oxygen vacancies.

Chiral induction enhanced photocatalytic degradation of methyl orange by Ag@Ag3PO4 and the reaction mechanism

A novel chiral Ag@Ag3PO4-NaDC composite was synthesized by chiral induction. SEM, XRD, CD spectrum, FTIR, UV–vis and XPS were used to study the physical and chemical properties of the materials, and the photocatalytic oxidation ability was evaluated with methyl orange as the target pollutant. The results show that the introduction of chirality can obviously promote the light absorption ability, broaden the band gap, enhance the oxidation ability, promote the separation of electrons and holes, greatly enhance the plasma resonance effect of silver nanoparticles, and promote the synergistic effect between silver nanoparticles and silver phosphate. Compared with Ag@Ag3PO4, the catalytic degradation ability of chiral Ag@Ag3PO4-NaDC is improved by more than 60%. Therefore, the chiral Ag@Ag3PO4-NaDC composite exhibits excellent photocatalytic performance. In the degradation of methyl orange by Ag@Ag3PO4-NaDC, a large amount of ·O2- and h+ were formed on the surface, which was the main reason for the oxidation ability.

The research on photocatalytic oxygen evolution of Bi4Ti3O12 microsphere by different Ag-loading content

The search of catalysts with high efficiency for photocatalytic oxygen evolution by water splitting has always attracted great attention of global scientists. In this study, Ag/Bi4Ti3O12 (Ag/BTO) nanocomposites with surface plasmon resonance (SPR) effect were synthesized by a solvothermal method. Compared with BTO, Ag/BTO narrowed the band gap, improved the absorption intensity in 400–700 nm region, increased the separation efficiency of photo-induced electron-hole pairs, reduced the energy barrier (from 2.18 to 1.39 eV) of the key step (O* → OOH*) from water splitting, and remarkably enhanced the photocatalytic water oxidation ability. The oxygen evolution rate of visible-light-driven 3-Ag/BTO with an appropriate silver content is 2623.51 μmol∙g−1∙h−1, which is 8.39 times higher than that of BTO without any sacrificial agent. Moreover, the excellent performance of 3-Ag/BTO is also obviously higher than that of most reported photocatalysts.

Ag3PO4-anchored La2Ti2O7 nanorod as a Z-Scheme heterostructure composite with boosted photogenerated carrier separation and enhanced photocatalytic performance under natural sunlight

Developing wide spectra-responsive photocatalysts has attracted considerable attention in the photocatalytic technology to achieve excellent catalytic activity. Ag3PO4, with strong response to light spectra shorter than 530 nm, shows extremely outstanding photocatalytic oxidation ability. Unfortunately, the photocorrosion of Ag3PO4 is still the biggest obstacle to its application. Herein, the La2Ti2O7 nanorod was used to anchor Ag3PO4 nanoparticles in this study, and a novel Z-Scheme La2Ti2O7/Ag3PO4 heterostructure composite was constructed. Remarkably, the composite showed strong responsive to most of the spectra in natural sunlight. The Ag0 formed in-situ acted as the recombination center of photogenerated carriers, which promoted their efficient separation and contributed to the improved photocatalytic performance of the heterostructure. When the mass ratio of Ag3PO4 in the La2Ti2O7/Ag3PO4 catalyst was 50%, the degradation rate constant of Rhodamine B (RhB), methyl orange (MO), chloroquine phosphate (CQ), tetracycline (TC), and phenol under natural sunlight irradiation were 0.5923, 0.4463, 0.1399, 0.0493, and 0.0096 min−1, respectively. Furthermore, the photocorrosion of the composite was greatly inhibited, 76.49% of CQ and 83.96% of RhB were still degraded after four cycles. Besides, the holes and O2•− played a significant role in RhB degradation, and it included multiple mechanisms of deethylation, deamination, decarboxylation, and cleavage of ring-structures. Moreover, the treated solution can also show safety to the water receiving environment. Overall, the synthesized Z-Scheme La2Ti2O7/Ag3PO4 composite exhibited immense potential for removing various organic pollutants through photocatalytic technology under natural sunlight irradiation.

Molecular Dipole Modulation of Porphyrins to Enhance Photocatalytic Oxidation Activity for Inactivation of Intracellular Bacteria.

The regulation of molecular structures of porphyrin-based photosensitizers is crucial for yielding the effective singlet oxygen as one of the efficient photocatalytic reactive oxidation species. Here, we select methoxy substitution as an electron donor to decorate the porphyrin rings. Introducing a series of metal ions into porphyrin centers further prepares the methoxy-substituted metalloporphyrins (MPs, M = Co, Ni, Cu, Zn), with the hope of modulating their molecular dipole moments and photocatalytic activity. The theoretical calculation analyses show that the metal-free porphyrin center possesses a higher transition dipole and more delocalized orbitals, leading to efficient charge transfer and improved photocatalytic activity. The metalloporphyrin samples are then polymerized by poly(D, l-lactide-co-glycolide) to be applied to in vitro sterilization experiments. As expected, metal-free porphyrin has good antibacterial ability and good biocompatibility. Moreover, the highly effective bacteriostatic metal-free porphyrin achieves satisfactory photodynamic therapeutic outcomes against intracellular pathogens in cancer cells. This work demonstrates that the molecular dipole modulation of porphyrins is critical for their photocatalytic oxidation and antibacterial ability.

Bandgap widening through doping for improving the photocatalytic oxidation ability of narrow-bandgap semiconductors.

The trade-off relationship between narrowing the bandgap and achieving sufficient redox potentials accounts for the hindrance to the development of an efficient photocatalyst. Most of the previous researchers attempt to narrow the bandgap of semiconductors by impurity doping to achieve visible-light sensitivity, but this approach causes the losses of their oxidation and/or reduction ability. Conversely, this study presents a bandgap widening strategy by doping to improve the redox potential of photogenerated carriers. Employing first-principles simulations, we propose the lanthanum-doped bismuth vanadate (La-BiVO4) photocatalyst as a wider-bandgap semiconductor exhibiting stronger oxidation ability compared to pristine BiVO4, and the results revealed that the bismuth orbital in the valence band (VB) was diluted by lanthanum-ion doping, while the VB shifted to a higher potential (positively shifted). Thereafter, a La-BiVO4 powder was synthesized via a solid-state reaction, after which its activity was evaluated in the photocatalytic oxidation of 2-propanol (IPA). La-BiVO4 exhibited bandgap widening; thus, the number of absorbed photons under visible-light irradiation was lower than that of pristine BiVO4. However, the quantum efficiency (QE) of La-BiVO4 for the oxidation of IPA was higher than that of the pristine BiVO4. Consequently, the photocatalytic reaction rate of La-BiVO4 was superior to that of pristine BiVO4 under the same visible-light irradiation conditions. Although the bandgap of La-BiVO4 is widened, it is still sensitive to the cyan-light region, which is the strongest in the sunlight spectrum. These results demonstrate that the orbital dilution strategy by impurity elemental doping is effective for bandgap widening and contributes to improving the oxidation and/or reduction ability of the photogenerated charge carriers. This study elucidates the possibility of boosting photocatalytic performances via bandgap widening.

Synthesis, Characterization and Photocatalytic Properties of Metal Phthalocyanine Modified Thermoresponsive Polymers

In this study, 3-hydroxyethoxyphenyl-9(10), 16(17), 23 (24)-decyloxy-zinc phthalocyanine (HDPcZn) was first prepared by liquid phase catalysis, and then it was esterified with Poly-(N-isopropylacrylamide) which have two carboxyl groups (TRIT-PNIPAM) at the end to obtain a linear thermoresponsive polymer (PcZn-PNIPAM-PcZn) with two phthalocyanines at the end. The polymer was characterized by FT-IR, 1H NMR, EDS and UV-vis, and the photocatalytic performance of the polymer was tested with 1,5-dihydroxynaphthalene (DHN) as a model pollutant. The results showed that PcZn-PNIPAM-PcZn exhibited excellent photocatalytic oxidation ability for DHN under visible light irradiation (2h, 78.1 %).

Ti3C2 MXene assembled with TiO2 for efficient photocatalytic mineralization of gaseous o-xylene

In the research of photocatalytic removal of VOCs, the mineralization rate of organic pollutants has been ignored. High mineralization rate means the reduction of intermediates, which is more conducive to environmental protection and photocatalysts stability. In this work, we successfully compounded conductive Ti3C2 with TiO2 for photocatalytic degradation of o-xylene. The production of CO2 by 1 % Ti3C2-TiO2 composite was about twice than that of pure TiO2. The results of PL and photocurrent response showed that 1 % Ti3C2-TiO2 composite had less carrier recombination and higher photocurrent response, which endows its stronger photocatalytic oxidation ability than TiO2. The in-situ infrared spectroscopy revealed that more aromatic anhydride species deposited on the TiO2 surface and led to the less mineralization degree for TiO2 sample. The four-cycle tests further confirmed the better stability of 1 % Ti3C2-TiO2 sample. This work disclosed the role of Ti3C2 in enhancing the mineralization of VOCs, which may provide a new perspective for the design of high-efficiency photocatalysts.

High specific surface CeO2–NPs doped loose porous C3N4 for enhanced photocatalytic oxidation ability

Porous C3N4 (PCN) is favored by researchers because it has more surface active sites, higher specific surface area and stronger light absorption ability than traditional g–C3N4. In this study, cerium dioxide nanoparticles (CeO2–NPs) with mixed valence state of Ce3+ and Ce4+ were doped into the PCN framework by a two-step method. The results indicate that CeO2–NPs are highly dispersed in the PCN framework, which leads to a narrower band gap, a wider range of the light response and an improved the separation efficiency of photogenerated charge in PCN. Moreover, the specific surface area (145.69 m2 g−1) of CeO2–NPs doped PCN is a 25.5% enhancement than that of PCN (116.13 m2 g−1). In the experiment of photocatalytic selective oxidation of benzyl alcohol, CeO2–NPs doped porous C3N4 exhibits excellent photocatalytic activity, especially Ce–PCN–30. The conversion rate of benzyl alcohol reaches 74.9% using Ce–PCN−30 as photocatalyst by 8 h of illumination, which is 25.7% higher than that of pure porous C3N4. Additionally, CeO2–NPs doped porous C3N4 also exhibits better photocatalytic efficiency for other aromatic alcohols.

The Photocatalytic Oxidation Ability of Rb0.9nb1.625mo0.375o5.62 Β-Pyrochlore Compound with Cubic Structure

The Photocatalytic Oxidation Ability of Rb0.9nb1.625mo0.375o5.62 Β-Pyrochlore Compound with Cubic Structure

Visible-light activation of sulfite by ZnFe2O4@PANI photocatalyst for As(III) removal: The role of radicals and Fe(IV)

Inorganic arsenic (As) exists widely in industrial wastewater and poses a serious risk to human health. Here, sulfite was employed to enhance the photocatalytic oxidation ability, and As(III) containing wastewater was rapidly purified within 30 min. Furthermore, this photocatalytic system maintain excellent performance at wide pH range of 3–10. By measuring intermediate radicals and ions, pH-dependent mechanism of sulfite activation was proposed. Under acid conditions, sulfite radicals (•SO3-) were detected in photocatalytic system, and quickly convert into oxidizing radicals (•SO4- and •OH), which were responsible for As(III) oxidation. While at alkaline conditions, only tetravalent iron [Fe(IV)] was detected as oxidizing substance contributing to As(III) removal during photo reaction process. Moreover, Fe(IV) mainly existed on catalyst surface rather than solution, the limited Fe leaching could extend the service life of catalyst, which should be attributed to the core–shell structure of ZnFe2O4@PANI. These findings in this work advances the fundamental understanding of radicals conversion and Fe(IV) formation during sulfite activation process.

Nanospatial Charge Modulation of Monodispersed Polymeric Microsphere Photocatalysts for Exceptional Hydrogen Peroxide Production.

Photocatalysis offers a sustainable strategy for hydrogen peroxide (H2 O2 ) production, which is an essential oxidant and emerging energy carrier in modern chemical industry. The development of polymer-based photocatalysts to produce H2 O2 has great potential but is limited by lower efficiency due to the limitation of light utilization and the low charge separation efficiency. Herein, a series of monodispersed mesoporous resorcinol-formaldehyde resin spheres (MRFS) are reported with a rational designed spatial charge distribution, exhibiting wide light absorption with a solar-to-chemical conversion (SCC) efficiency of 1.1%. Surface photovoltage microscopy (SPVM) measurements unraveled the charge separation in nanospace with uneven distribution of donor (D) and acceptor (A) sites. A density functional theory (DFT) calculation elucidated the origin of photogenerated electrons and holes. Moreover, MRFS demonstrates photocatalytic water oxidation ability. The findings in this work open a new avenue for the development of porous polymeric photocatalysts toward highly efficient solar energy conversion.

Prolonging lifetime of photogenerated carriers in WO3 nanowires by oxygen vacancies engineering for enhanced photoelectrocatalytic oxygen evolution reaction

WO3 nanowires (NWs) have emerged as a promising alternative electrocatalyst for the photoelectrochemical (PEC) oxygen evolution reaction (OER), due to their nontoxicity, low cost, good stability, and strong photocatalytic oxidation ability. However, a significant challenge is limited by the poor electrical conductivity and the rapid recombination rate of photogenerated carriers. This paper reports a facile and effective way to synthesize the WO3 NWs with oxygen vacancies (Ov-WO3 NWs), which have high PEC OER activity and good stability. Photoelectric measurements indicate that the Ov-WO3 NW-based device shows a good light-harvesting property under visible light and a prolonged photoresponse time. Electrochemical impedance spectra measurements reveal a reduced value of Rct denoting an improved electrical conductivity, which should be responsible for the superior PEC OER performance. Our work provides a strategy for fabricating efficient water-splitting electrodes to help establish rational design principles for future OER catalysts.

Surface oxygenous groups modified graphitic carbon nitride with significant positive shift of valence band for efficient photocatalytic oxidation

Graphitic carbon nitride (g-C3N4) is a remarkable metal-free photocatalyst which is widely used for photocatalytic reductive reaction due to its suitable potential of conduction band, but also suffers from intrinsically weak photocatalytic oxidation ability. Here, by simply refluxing g-C3N4 in H2O2, oxygenous groups are introduced into g-C3N4. The resultant oxygenous groups modified g-C3N4 (g-C3N4(H2O2)) exhibits significantly improved hydrophilic ability and photocatalytic oxidative ability. It is well evidenced that valence band position is positive shifted significantly by introduction of surface oxygenous groups. However, the photocatalytic activity for oxygen evolution is not improved obviously, suggesting that the driving force for water oxidation is not increased simultaneously. Luckily, the photocatalytic oxidative activity of the modified g-C3N4 (include oxygen evolution, pollutant degradation and antibacterial property) could be further improved after forming TiO2-containing nanocomposites during the H2O2 reflux treatment with the addition of tertrabutyl titanate (g-C3N4/TiO2(H2O2) due to much increased driving force and accelerated charge migration. Herein, a facile and simple method is proposed to engineer the band structure of g-C3N4 for improving its photocatalytic oxidative ability, which expand the application of carbon nitride.

Synthesis of Carbon Nitride Intercalation Compound Composite and Study of Visible Light-Induced Photocatalytic Performance

Novel visible light-induced carbon nitride intercalation compound (CNIC) with iron oxide composite photocatalyst with different content of iron oxide were synthesized through simple mixing and heat treatment. The composite photocatalyst was characterized by Fourier transform infrared (FT-IR) spectroscopy and BET surface area measurements. The photocatalytic oxidation ability of the novel composite photocatalyst was evaluated using methyl range (MO) as a target pollutant. The experimental results showed the composites with a content of iron oxide exhibited the higher photocatalytic activity than either single-phase iron oxide or CNIC under visible-light irradiation. The as-prepared composite photocatalyst exhibits an improved photocatalytic activity due to enhancement of photo-generated electron–hole separations at the interface.

First-principles of Be/Mg/Ca doping and point defects of VZn and Hi in the magnetic and optical properties of ZnO

The effects of Be/Mg/Ca doping and the coexistence of Zn vacancies in the magnetic and optical properties of ZnO have been widely reported, but the previous studies have neglected the influence of the H interstitial on the doping system. The source and mechanism of magnetism caused by O ions in the doping system remain unclear, and no reasonable theoretical explanation has been proposed thus far. As a point defect, Zn vacancies are hard to precisely control in experiments. In view of solving this problem, this study uses the first principles under the framework of density functional theory to investigate the effects of the single doping of Be, Mg, and Ca and the coexistence of Zn vacancies and H interstitial in the magnetic and optical properties of ZnO. Findings indicate that the bulk moduli of all doped systems are reduced with respect to that of the undoped Zn36O36. Apart from the O2− ions, some O1− ions exist in all doping systems. The O1− ions containing itinerant electrons are the main source of O ion magnetism in the doping system. The formation energy of the Zn34MHiO36 (M = Be/Mg/Ca) system is lower than that of the Zn34MO36 (M = Be/Mg/Ca) system. Findings indicate that the doping of the H interstitial can reduce the formation energy of the Zn34MO36 (M = Be/Mg/Ca) system, allowing the system to become even more stable. The Zn34BeHiO36 system has the smallest formation energy. The Zn34BeHiO36, Zn34MgHiO36, and Zn34CaHiO36 systems all exhibit magnetism. The carriers’ activity in the photocatalyst, the visible light effect, the separation and lifetime of the carriers, and the photocatalytic oxidation ability are also considered in this research. Compared with the other configurations, the Zn34MgHiO36 system is more stable than the other systems, and it has a longer electron lifetime, stronger electric dipole moment, more obvious absorption spectral red shift, and stronger reduction ability. Therefore, the Zn34MgHiO36 system is the best choice for photocatalysis in H production. This research offers certain theoretical reference value for the design and preparation of new magneto-optical functional materials.