Synthesis of Pt-Loaded Self-Interspersed Anatase TiO2 with a Large Fraction of (001) Facets for Efficient Photocatalytic Nitrobenzene Degradation

Recent advances on catalysts for photocatalytic selective hydrogenation of nitrobenzene to aniline

Selective hydrogenation of nitrobenzene (SHN) is an important approach to synthesize aniline, an essential intermediate with extremely high research significance and value in the fields of textiles, pharmaceuticals and dyes. SHN reaction requires high temperature and high hydrogen pressure via the conventional thermal-driven catalytic process. On the contrary, photocatalysis provides an avenue to achieve high nitrobenzene conversion and high selectivity towards aniline at room temperature and low hydrogen pressure, which is in line with the sustainable development strategies. Designing efficient photocatalysts is a crucial step in SHN. Up to now, several photocatalysts have been explored for photocatalytic SHN, such as TiO2, CdS, Cu/graphene and Eosin Y. In this review, we divide the photocatalysts into three categories based on the characteristics of the light harvesting units, including semiconductors, plasmonic metal-based catalysts and dyes. The recent progress of the three categories of photocatalysts is summarized, the challenges and opportunities are pointed out and the future development prospects are described. It aims to give a clear picture to the catalysis community and stimulate more efforts in this research area.

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

A critical review of different prominent nanotechnologies adapted to catalysis is provided, with focus on how they contribute to the improvement of selectivity in heterogeneous catalysis. Ways to modify catalytic sites range from the use of the reversible or irreversible adsorption of molecular modifiers to the immobilization or tethering of homogeneous catalysts and the development of well-defined catalytic sites on solid surfaces. The latter covers methods for the dispersion of single-atom sites within solid supports as well as the use of complex nanostructures, and it includes the post-modification of materials via processes such as silylation and atomic layer deposition. All these methodologies exhibit both advantages and limitations, but all offer new avenues for the design of catalysts for specific applications. Because of the high cost of most nanotechnologies and the fact that the resulting materials may exhibit limited thermal or chemical stability, they may be best aimed at improving the selective synthesis of high value-added chemicals, to be incorporated in organic synthesis schemes, but other applications are being explored as well to address problems in energy production, for instance, and to design greener chemical processes. The details of each of these approaches are discussed, and representative examples are provided. We conclude with some general remarks on the future of this field.

Visible-light harvesting innovative W6+/Yb3+/TiO2 materials as a green methodology photocatalyst for the photodegradation of pharmaceutical pollutants

In this work, we report on the synthesis of a new-age reusable visible-light photocatalyst using a heterojunction nanocomposite of W⁶⁺/Yb³⁺ on a mixed-phase mesoporous network of monolithic TiO₂. The structural properties of the monolithic photocatalysts are characterized using p-XRD, SEM-EDAX, TEM-SAED, XPS, PLS, UV-Vis-DRS, FT-IR, micro-Raman, TG-DTA, and N₂ isotherm analysis. The electron microscopic analysis reveals a mesoporous network of ordered worm-like monolithic design, with a polycrystalline mixed-phase (anatase/rutile) TiO₂ composite, as indicated by diffraction studies. The UV-Vis-DRS analysis reveals a redshift in the light absorption characteristics of the mixed-phase TiO₂ monolith as a function of W⁶⁺/Yb³⁺ co-doping. It is observed that the use of (8.0 mol%)W⁶⁺/0.4 (mole%)Yb³⁺ co-doped monolithic TiO₂ photocatalyst, with an energy bandgap of 2.77 eV demonstrates superior visible-light photocatalysis, which corroborates with the PLS studies in terms of voluminous e^-/h⁺ pair formation. The practical application of the photocatalyst has been investigated through a time-dependent dissipation of enrofloxacin, a widely employed antimicrobial drug, and its degradation pathway has been monitored by LC-MS-ESI and TOC analysis. The impact of physio-chemical parameters such as solution pH, sensitizers, drug concentration, dopant/codopant stoichiometry, catalyst quantity, and light intensity has been comprehensively studied to monitor the process efficiency.

Preparation of a Novel Cellulose-Styrene Copolymer Adsorbent and Its Adsorption of Nitrobenzene from Aqueous Solutions

A novel cellulose–styrene copolymer adsorbent (cellulose-St) was prepared using free radical polymerization. Successful polymerization was confirmed through Fourier Transform Infrared Spectroscopy (FTIR), Carbon 13 Solid Nuclear Magnetic Resonance (¹³C NMR) Spectroscopy, Scanning Electron Microscopy (SEM), etc. Cellulose-St possessed good hydrophobicity, and the best water contact angle of cellulose-St samples could reach 146°. It had the ability of adsorption for nitrobenzene (NB), and the adsorption process could be well described by the pseudo-second-order (R² > 0.99) and three-stage intraparticle diffusion (R² > 0.99) kinetic models. Furthermore, the dynamic adsorption experiments revealed that cellulose-St had the potential for continuous separation of NB in water, and the breakthrough point for the initial NB concentration of 10 mg/L reached 1.275 L/g. Moreover, cellulose-St exhibited excellent environmental adaptability that it could maintain its hydrophobicity and adsorption ability for NB in strong acids, strong alkalis, or organic solvents. The used cellulose-St could be reused after washing with ethanol and keep almost constant adsorption capacity after ten cycles.

Photocatalytic treatment of tetracycline antibiotic wastewater by silver/TiO2 nanosheets/reduced graphene oxide and artificial neural network modeling

In this work, we focused on facile preparation of ternary nanocomposites containing TiO₂ nanosheets, reduced graphene oxide, and different quantities of silver for photocatalytic treatment of tetracycline (TC) antibiotic wastewater. Plasmonic silver nanoparticles were deposited on TiO₂ nanosheets/reduced graphene oxide nanocomposite via a photodeposition method (TGA(x) samples). The as-obtained samples were identified by variety of techniques such as XRD, UV-Vis DRS, FESEM/EDX, TEM, and Raman spectroscopy. The photocatalytic degradation experiments of TC (in concentration of 30 mg/L) were carried out by synthesized nanocomposites, and the degradation efficiency of TGA (0.076) (the optimal sample) was evaluated as 52.56% after 3 hr of irradiation under visible light. The obtained results showed that in TGA(x) samples, the reduced graphene oxide acts as a bridge for transferring photoinduced electrons from plasmonic silver nanoparticles to TiO₂ nanosheetes. A three-layered artificial neural network model with four input variables (irradiation time, catalyst dosage, initial concentration of TC, and silver nitrate content) and one output variable (% degradation) was optimized with 11 hidden neurons. The relative importance of the independent variables was calculated using Garson formula and the initial concentration of TC was found as the most influencing parameter (relative importance of 31%) on the treatment efficiency. PRACTITIONER POINTS: TiO₂ nanosheets synthesized on the reduced graphene oxide by hydrothermal method. Plasmonic silver nanoparticles deposited on TNs/rGO by photodeposition method The photocatalytic degradation of tetracycline (TC) was modeled by artificial neural network.

Role of reactive oxygen species on the activity of noble metal-doped TiO2 photocatalysts

Modified TiO₂ catalysts are of interest in environmental water remediation since they can lead to efficient electron-hole separation and greatly enhance the photocatalytic properties of TiO₂. Reactive oxygen species (ROS), such as the superoxide radical (O₂^-), hydroxyl radical (OH), and positive valence band holes (h⁺_VB), have been reported as the main oxidative species involved in photocatalytic degradation processes. In this work, the role of these species using TiO₂, TiO₂/Pt 0.5 wt%, and TiO₂/Ag 10 wt% has been examined in order to clarify the oxidation pathways. For this purpose, the contribution of the main oxidative species was analyzed in the photocatalytic degradation of dichloroacetic acid (DCA) solutions using specific scavengers (benzoquinone, tert-butyl alcohol, and formic acid). Moreover, the hydroxyl radicals were quantitatively determined in order better understand the results. Regardless of the catalyst used, it is concluded that OH radicals are the major reactive species responsible for DCA degradation and no significant degradation is due to O₂^- radicals. Nevertheless, different OH generation pathways were found, depending on the nature of the catalysts. Degradation using TiO₂ was conducted mainly via OH radicals generated in the positive holes, while noble metal-doped TiO₂ catalysts generated OH radicals through the transformation of O₂^- radicals.

Light-driven nitrous oxide production via autotrophic denitrification by self-photosensitized Thiobacillus denitrificans

N₂O (Nitrous oxide, a booster oxidant in rockets) has attracted increasing interest as a means of enhancing energy production, and it can be produced by nitrate (NO₃^-) reduction in NO₃^--loading wastewater. However, conventional denitrification processes are often limited by the lack of bioavailable electron donors. In this study, we innovatively propose a self-photosensitized nonphototrophic Thiobacillus denitrificans (T. denitrificans-CdS) that is capable of NO₃^- reduction and N₂O production driven by light. The system converted >72.1 ± 1.1% of the NO₃^--N input to N₂ON, and the ratio of N₂O-N in gaseous products was >96.4 ± 0.4%. The relative transcript abundance of the genes encoding the denitrifying proteins in T. denitrificans-CdS after irradiation was significantly upregulated. The photoexcited electrons acted as the dominant electron sources for NO₃^- reduction by T. denitrificans-CdS. This study provides the first proof of concept for sustainable and low-cost autotrophic denitrification to generate N₂O driven by light. The findings also have strong implications for sustainable environmental management because the sunlight-triggered denitrification reaction driven by nonphototrophic microorganisms may widely occur in nature, particularly in a semiconductive mineral-enriched aqueous environment.

Facet-Dependent Photocatalytic Behaviors of ZnS-Decorated Cu2O Polyhedra Arising from Tunable Interfacial Band Alignment

ZnS particles were grown over Cu₂O cubes, octahedra, and rhombic dodecahedra for examination of their facet-dependent photocatalytic behaviors. After ZnS growth, Cu₂O cubes stay photocatalytically inactive. ZnS-decorated Cu₂O octahedra show enhanced photocatalytic activity, resulting from better charge carrier separation upon photoexcitation. Surprisingly, Cu₂O rhombic dodecahedra give greatly suppressed photocatalytic activity after ZnS deposition. Electron paramagnetic resonance spectra agree with these experimental observations. Time-resolved photoluminescence profiles provide charge-transfer insights. The decrease in the photocatalytic activity is attributed to an unfavorable band alignment caused by significant band bending within the Cu₂O(110)/ZnS(200) plane interface. A modified Cu₂O-ZnS band diagram is presented. Density functional theory calculations generating plane-specific band energy diagrams of Cu₂O and ZnS match well with the experimental results, showing that charge transfer across the Cu₂O(110)/ZnS(200) plane interface would not happen. This example further illustrates that the actual photocatalysis outcome for semiconductor heterojunctions cannot be assumed because interfacial charge transfer is strongly facet-dependent.

Active {001} Facet Exposed TiO2 Nanotubes Photocatalyst Filter for Volatile Organic Compounds Removal: From Material Development to Commercial Indoor Air Cleaner Application

TiO₂ nanotubes (TNT) have a highly ordered open structure that promotes the diffusion of dioxygen and substrates onto active sites and exhibit high durability against deactivation during the photocatalytic air purification. Herein, we synthesized {001} facet-exposed TiO₂ nanotubes (001-TNT) using a new and simple method that can be easily scaled up, and tested them for the photocatalytic removal of volatile organic compounds (VOCs) in both a laboratory reactor and a commercial air cleaner. While the surface of TNT is mainly composed of {101} facet anatase, 001-TNT's outer surface was preferentially aligned with {001} facet anatase. The photocatalytic degradation activity of toluene on 001-TNT was at least twice as high as that of TNT. While the TNT experienced a gradual deactivation during successive cycles of photocatalytic degradation of toluene, the 001-TNT did not exhibit any sign of catalyst deactivation under the same test conditions. Under visible light irradiation, the 001-TNT showed degradation activity for acetaldehyde and formaldehyde, while the TNT did not exhibit any degradation activity for them. The 001-TNT filter was successfully scaled up and installed on a commercial air cleaner. The air cleaner equipped with the 001-TNT filters achieved an average VOCs removal efficiency of 72% (in 30 min of operation) in a 8-m³ test chamber, which satisfied the air cleaner standards protocol (Korea) to be the first photocatalytic air cleaner that passed this protocol.

Mechanistic insights into plasmonic photocatalysts in utilizing visible light

The utilisation of sunlight as an abundant and renewable resource has motivated the development of sustainable photocatalysts that can collectively harvest visible light. However, the bottleneck in utilising the low energy photons has led to the discovery of plasmonic photocatalysts. The presence of noble metal on the plasmonic photocatalyst enables the harvesting of visible light through the unique characteristic features of the noble metal nanomaterials. Moreover, the formation of interfaces between noble metal particles and semiconductor materials further results in the formation of a Schottky junction. Thereby, the plasmonic characteristics have opened up a new direction in promoting an alternative path that can be of value to the society through sustainable development derived through energy available for all for diverse applications. We have comprehensively prepared this review to specifically focus on fundamental insights into plasmonic photocatalysts, various synthesis routes, together with their strengths and weaknesses, and the interaction of the plasmonic photocatalyst with pollutants as well as the role of active radical generation and identification. The review ends with a pinnacle insight into future perspectives regarding realistic applications of plasmonic photocatalysts.

A novel Ag(i)-calix[4]arene coordination polymer for the sensitive detection and efficient photodegradation of nitrobenzene in aqueous solution

Nitrobenzene (NB) is a widespread and highly toxic organic pollutant in water, and consequently its detection and removal have attracted considerable attention. In the present study, we designed and synthesized a novel coordination polymer, [AgL_0.5(NO₃)]_n (1), {L = 25,26,27,28-tetra[(3-pyridylmethyl)oxy]calix[4]arene}, from AgNO₃ and a tetra-pyridyl-functionalized calix[4]arene ligand, which possessed a 2D network based on [Ag₄L(NO₃)₄] units. The 1-modified glassy carbon electrode (1/GCE) exhibited good electrocatalytic activity toward the reduction of NB, offering the selective detection of NB in a wide linear range (1-2450 μM) and a low detection limit (0.62 μM). Furthermore, it displayed excellent photocatalytic activity for the degradation of NB in aqueous solution under UV light. The kinetics of the catalytic degradation reaction and the stability of the catalyst were also studied. These results indicated that compound 1 is a favorable material for the effective determination and degradation of NB, which makes it a promising candidate in both monitoring water quality and treating wastewater.

Structure sensitive photocatalytic reduction of nitroarenes over TiO 2

It is a subject of exploration whether the phase pure anatase or rutile TiO₂ or the band alignment due to the heterojunctions in the two polymorphs of TiO₂ plays the determining role in efficacy of a photocatalytic reaction. In this work, the phase pure anatase and rutile TiO₂ have been explored for photocatalytic nitroarenes reduction to understand the role of surface structures and band alignment towards the reduction mechanism. The conduction band of synthesized anatase TiO₂ has been found to be more populated with electrons of higher energy than that of synthesized rutile. This has given the anatase an edge towards photocatalytic reduction of nitroarenes over rutile TiO₂. The other factors like adsorption of the reactants and the proton generation did not play any decisive role in catalytic efficacy.

Structure sensitive photocatalytic reduction of nitroarenes over TiO 2

It is a subject of exploration whether the phase pure anatase or rutile TiO₂ or the band alignment due to the heterojunctions in the two polymorphs of TiO₂ plays the determining role in efficacy of a photocatalytic reaction. In this work, the phase pure anatase and rutile TiO₂ have been explored for photocatalytic nitroarenes reduction to understand the role of surface structures and band alignment towards the reduction mechanism. The conduction band of synthesized anatase TiO₂ has been found to be more populated with electrons of higher energy than that of synthesized rutile. This has given the anatase an edge towards photocatalytic reduction of nitroarenes over rutile TiO₂. The other factors like adsorption of the reactants and the proton generation did not play any decisive role in catalytic efficacy.

Encapsulating nano rods of copper–biphenylamines framework on g-C3N4 photocatalysts for visible-light-driven organic dyes degradation: promoting charge separation efficiency

For the first time we have successfully constructed semi conductive copper–biphenylamines framework hybrid photocatalysts to degrade organic pollutants.

RGO/TiO2 nanosheets immobilized on magnetically actuated artificial cilia film: a new mode for efficient photocatalytic reaction

Exploring a proper mode for practical reaction and efficient recycle has been an extensively studied subject in the photocatalysis field.

Transparent Nb-doped TiO2 films with the [001] preferred orientation for efficient photocatalytic oxidation performance

[001]-Oriented Nb-TiO₂ films via topotactic transformation from [100]-oriented Nb-TiN exhibit efficient photoactivity due to highly-reactive-facet exposure and increased surface-reactive sites.

Light-induced spatial separation of charges toward different crystal facets of square-like WO3

Light-induced preferential migration of electrons and holes to the minor (200) and (020) facets and the dominant (002) facets of square-like WO₃, respectively, resulted in the square-like WO₃ nanoplates with Pt loaded mainly on dominant (002) facets shows higher photocatalytic activity than that Pt loaded on the minor facets.

New insight on facet-dependent physicochemical properties of anatase TiO2 nanostructures for efficient photocatalysis

Crystal growth mechanisms and physicochemical properties associated with the photocatalytic activities have been systematically investigated.

Ni2+ and Ti3+ co-doped porous black anatase TiO2 with unprecedented-high visible-light-driven photocatalytic degradation performance

A black Ni doped porous TiO₂ were fabricated via an in situ solid-state chemical reduction approach, which exhibited excellent visible-light-driven performance.