Structurally and surficially activated TiO2 nanomaterials for photochemical reactions

Renewable fuels and environmental remediation are of paramount importance in today's world due to escalating concerns about climate change, pollution, and the finite nature of fossil fuels. Transitioning to sustainable energy sources and addressing environmental pollution has become an urgent necessity. Photocatalysis, particularly harnessing solar energy to drive chemical reactions for environmental remediation and clean fuel production, holds significant promise among emerging technologies. As a benchmark semiconductor in photocatalysis, TiO2 photocatalyst offers an excellent solution for environmental remediation and serves as a key tool in energy conversion and chemical synthesis. Despite its status as the default photocatalyst, TiO2 suffers from drawbacks such as a high recombination rate of charge carriers, low electrical conductivity, and limited absorption in the visible light spectrum. This review provides an in-depth exploration of the fundamental principles of photocatalytic reactions and presents recent advancements in the development of TiO2 photocatalysts. It specifically focuses on strategic approaches aimed at enhancing the performance of TiO2 photocatalysts, including improving visible light absorption for efficient solar energy harvesting, enhancing charge separation and transportation efficiency, and ensuring stability for robust photocatalysis. Additionally, the review delves into the application of photodegradation and photocatalysis, particularly in critical processes such as water splitting, carbon dioxide reduction, nitrogen fixation, hydrogen peroxide generation, and alcohol oxidation. It also highlights the novel use of TiO2 in plastic polymerization and degradation, showcasing its potential for converting plastic waste into valuable chemicals and fuels, thereby offering sustainable waste management solutions. By addressing these essential areas, the review offers valuable insights into the potential of TiO2 photocatalysis for addressing pressing environmental and energy challenges. Furthermore, the review encompasses the application of TiO2 photochromic systems, expanding its scope to include other innovative research and applications. Finally, it addresses the underlying challenges and provides perspectives on the future development of TiO2 photocatalysts. Through addressing these issues and implementing innovative strategies, TiO2 photocatalysis can continue to evolve and play a pivotal role in sustainable energy and environmental applications.

Recent Advances in the Heterogeneous Photocatalytic Hydroxylation of Benzene to Phenol

Phenol is an important chemical material that is widely used in industry. Currently, phenol is dominantly produced by the well−known three−step cumene process, which suffers from severe drawbacks. Therefore, developing a green, sustainable, and economical strategy for the production of phenol directly from benzene is urgently needed. In recent years, the photocatalytic hydroxylation of benzene to phenol, which is economically feasible and could be performed under mild conditions, has attracted more attention, and development of highly efficient photocatalyst would be a key issue in this field. In this review, we systematically introduce the recent achievements of photocatalytic hydroxylation of benzene to phenol from 2015 to mid−2022, and various heterogeneous photocatalysts are comprehensively reviewed, including semiconductors, polyoxometalates (POMs), graphitic carbon nitride (g−C3N4), metal–organic frameworks (MOFs), carbon materials, and some other types of photocatalysts. Much effort is focused on the physical and chemical approaches for modification of these photocatalysts. The challenges and future promising directions for further enhancing the catalytic performances in photocatalytic hydroxylation of benzene are discussed in the end.

Pyrithione metal (Cu, Ni, Ru) complexes as photo-catalysts for styrene oxide production

Selective photochemical oxidation of styrene was performed in an active acetonitrile medium, using H₂O₂ with or without ultraviolet (UV) light radiation. Pyrithione metal complexes (M-Pth: M = Cu(II), Ni(II), Ru(II); Pth = 2-mercaptopyridine-N-oxide) were used as catalysts. Catalytic testing measurements were done by varying the time, chemical reaction temperature and H₂O₂ concentration with or without UV energy. Epoxide styrene oxide (SO), benzaldehyde and acetophenone were the major synthesized products. A high batch rate, conversion and selectivity towards SO was shown in the presence of UV. A minor constant formation of CO₂ was observed in the stream. Coordinated Ru-based compounds demonstrated the highest process productivity of SO at 60 °C. The effect of the functional alkyl substituent on the ligand Pth, attached to the specific ruthenium(II) centre, decreased the activity of the substance. Ni-Pth selectively yielded benzaldehyde. The stability of the catalysts was examined by applying nuclear magnetic resonance (NMR) spectroscopy and thermogravimetric analysis coupled with mass spectrometry. Tested metal complexes with pyrithione (M-Pth) exhibited excellent reuse recyclability up to 3 cycles.

Bimetallic Au-Pd nanoparticles supported on silica with a tunable core@shell structure: enhanced catalytic activity of Pd(core)-Au(shell) over Au(core)-Pd(shell)

A facile ligand-assisted approach of synthesizing bimetallic Au-Pd nanoparticles supported on silica with a tunable core@shell structure is presented. Maneuvering the addition sequence of metal salts, both Aucore-Pdshell (Au@Pd-SiO2) and Pdcore-Aushell (Pd@Au-SiO2) nanoparticles were synthesized. The structures and compositions of the core-shell materials were confirmed by probe-corrected HRTEM, TEM-EDX mapping, EDS line scanning, XPS, PXRD, BET, FE-SEM-EDX and ICP analysis. The synergistic potentials of the core-shell materials were evaluated for two important reactions viz. hydrogenation of nitroarenes to anilines and hydration of nitriles to amides. In fact, in both the reactions, the Au-Pd materials exhibited superior performance over monometallic Au or Pd counterparts. Notably, among the two bimetallic materials, the one with Pdcore-Aushell structure displayed superior activity over the Aucore-Pdshell structure which could be attributed to the higher stability and uniform Au-Pd bimetallic interfaces in the former compared to the latter. Apart from enhanced synergism, high chemoselectivity in hydrogenation, wide functional group tolerance, high recyclability, etc. are other advantages of our system. A kinetic study has also been performed for the nitrile hydration reaction which demonstrates first order kinetics. Evaluation of rate constants along with a brief investigation on the Hammett parameters has also been presented.

Efficient photocatalytic conversion of benzene to phenol on stabilized subnanometer WO3 quantum dots

Subnanometer WO3 quantum dots are spontaneously produced in a mesoporous silica matrix. Efficient photocatalytic conversion of benzene to phenol without decomposition of the product is realized by band engineering with a strong quantum size effect.

Polyoxometalates acting as a hole-transfer mediator and crystallization accelerant in a perovskite photoanode for the photoelectrocatalytic oxidation of benzene into phenol

Organic metal halide perovskite (OMHP) material shows promising applications in the photoelectrocatalytic field, but its efficiencies are unsatisfactory due to the bulk and surface carrier recombination. In this work, we used dual polyoxometalates (C₄H₉N)₃PW₁₂O₄₀ and [Ag₁₀[{Co(H₂O)₃}₂{CoBi₂W₁₉O₆₆(OH)₄}] to modify the OMHP photoanode; the former acted to improve the quality of the perovskite film and the latter could facilitate hole transfer. Such dual modifications effectively reduce carrier recombination and thus obviously boost photoelectrocatalytic efficiency. Hence, we explored the photoelectrocatalytic oxidation of benzene into phenol in aqueous solution by using the modified OMHP photoanode. The yield of phenol in the reaction using the modified OMHP photoanode reached about 31.8%, which was obviously superior to that using the pure OMHP photoanode. Furthermore, we carried out radical scavenger studies to investigate the active species involved in the photoelectrocatalytic benzene oxidation reaction, and thus proposed the plausible mechanism of the photoelectrocatalytic oxidation of benzene into phenol over the OMHP photoanode. These results provide new insights into the development of high performance OMHP photoanodes for photoelectrocatalytic organic transformation.

A hierarchical flower-like hollow alumina supported bimetallic AuPd nanoparticle catalyst for enhanced solvent-free ethylbenzene oxidation

Currently, oxidation of alkylaromatics is considered as one of the most crucial chemical technologies to produce high added-value alcohols, ketones and carboxylic acids, due to its significant importance both in fine synthetic chemistry and in the academic field. In this work, a novel hierarchical marigold-like hollow alumina supported bimetallic AuPd nanoparticle catalyst was successfully fabricated and employed for highly efficient solvent-free ethylbenzene oxidation to produce acetophenone with the coexistence of both molecular oxygen and tert-butyl hydroperoxide as the oxidant and the initiator. The as-fabricated bimetallic AuPd nanocatalyst conferred a superior catalytic performance to the corresponding monometallic counterparts and commercial Al2O3 or solid Al2O3 microsphere supported AuPd ones, along with a high acetophenone selectivity of 88.2% at a conversion of 50.9% under mild reaction conditions (120 °C and oxygen pressure of 1.0 MPa), as well as an unprecedentedly high turnover frequency value of 46 768 h-1. Such exceptional efficiency of the catalyst was related to both the significant synergy between the Au-Pd atoms and strong metal-support interactions, and the unique hierarchical micro/nanostructure of the support being beneficial to the close contact of reactants with surface adsorption and reaction sites and easy product diffusion. Moreover, the present bimetallic AuPd catalyst was recyclable and stable. The developed approach is expected to offer exciting opportunities for designing other supported monometallic or bimetallic catalysts with various active components applied in heterogeneous catalysis.

Degradation pathways of aniline in aqueous solutions during electro-oxidation with BDD electrodes and UV/H2O2 treatment

In this work, it has been studied the mineralization of aniline, a toxic substance of low biodegradability typically found in many industrial wastewaters, through electro-oxidation using boron doped diamond (BDD) electrodes and photo-oxidation (UV photolysis and UV/H₂O₂ treatments). It was observed that in electro-oxidation and UV/H₂O₂, it was feasible to reach aniline mineralizations higher than 85%. Two different degradation routes have been observed during the aniline oxidation in these two treatments. The first route was the mineralization pathway, in which aniline was oxidized to CO₂, water and nitrate. The second route was the polyaniline pathway in which polyanilines of high molecular weight are formed. The intermediate compounds involved in both degradation routes are different depending on the treatment used. In the electro-oxidation, denitrification processes were also observed. From an economical point of view, electro-oxidation of aniline using BDD electrodes is more interesting than UV/H₂O₂ due it has an 87% lower operational cost. So, electro-oxidation using BDD electrodes seems to be a more suitable technique for the mineralization of wastewater containing aniline than UV or H₂O₂ based technologies.

Treatment of Bronchopleural Fistula with Carbolic Acid instilled through Bronchofiberscope in post-pulmonectomy patients

OBJECTIVE

To investigate the efficacy of carbolic acid treatment of bronchopleural fistula (BPF) using bronchofiberscope (BFS) in post-pulmonectomy patients.

METHOD

Twelve patients with post-pulmonectomy BPF were enrolled in this study at the Liaoning Tumor Hospital between February 2009 and March 2012. Three patients had BPF after the right pneumonectomy, six patients after left pneumonectomy, one patient after the right middle and low lobectomy and two patients after left upper lobectomy. BPF patients were instilled with 100 % carbolic acid (0.5-1 ml one time every week) through BFS on the mucosal surface around the fistula, and the bubble disappearance was monitored. Treatment was repeated if the bubble remained.

RESULTS

No haemorrhage, severe dyspnea or SpO2 declines occurred in all the 12 patients during the bronchoscopic therapy. BPF orifices were closed in five patients after receiving 5 treatments with carbolic acid, 1 patient received 2 treatments, 1 patient was given 3 treatments, 2 patients received 4 treatments and 3 patients were given 7 treatments. Follow-up was conducted for six months following bronchoscopy. The average treatment and fistula closure time were calculated from the data collected as 20 min and 30 days, respectively, and the cure rate was 100 %. Hematoxylin-eosin (HE) staining results revealed that the white flat hyperplasia tissue after carbolic acid treatment was inflammatory granulation tissue.

CONCLUSION

Our results revealed that instillation of 100 % carbolic acid with BFS to treat BPF was 100 % effective, which can be a support for post-pulmonectomy BPF.

Optimised photocatalytic hydrogen production using core–shell AuPd promoters with controlled shell thickness

AuPd shell–Au core promoters with controlled shell thickness supported on titanium dioxide improve the photocatalytic hydrogen production.