The shifting research landscape for PAH bioremediation in water environment: a bibliometric analysis on three decades of development.

Polycyclic aromatic hydrocarbons (PAHs) with their carcinogenic, teratogenic, and mutagenic effects can cause great damage to the ecosystem and public health when present in water. With bioremediation, PAH contamination in water environment can be greatly reduced in an eco-friendly manner. It has thus become the research focus for many environmental scientists. In this study, a bibliometric analysis on three-decade (1990-2022) development of PAH bioremediation in water environment was conducted from temporal and spatial dimensions using CiteSpace. A total of 2480 publications, obtained from Web of Science core collection database, were used to explore the basic characteristics, hotspots, and prospects of the research area. The results showed that (1) bioremediation/biodegradation of PAHs in water environment has been getting researchers' attention since 1990, and is gaining even more traction as time goes on. (2) In terms of countries, China and the USA were the major contributors in this research area, while at the institutional level, the Chinese Academy of Sciences has produced the most research results. However, international cooperation across regions was lacking in the field. (3) Environment Science and Technology, Chemosphere, Applied and Environment Microbiology, Journal of Hazardous Materials, and Environment Pollution were the 5 most cited journals in this field. (4) There were three major stages the field has gone through, each with distinct research hotspots, including initial stage (1990-1994), mechanism investigation (1995-2000), and application exploration (2001-2010; 2011-2022). Finally, research perspectives were proposed, covering three directions, namely, bioavailability, immobilization, and viable but nonculturable (VBNC) bacteria.

Simultaneous Realization of Enhanced Photoactivity and Promoted Photostability by Multilayered MoS2 Coating on CdS Nanowire Structure via Compact Coating Methodology.

CdS has been regarded as a promising photocatalytic water-splitting visible-light photocatalyst, but low catalytic activity and photocorrosion seriously limited its practical application. Here, inspired by core-shell principles, we try to fabricate CdS@MoS2 core-shell structures by utilizing unstable CdS nanowires as core and multilayered MoS2 as shell. Multilayered MoS2 not only serves as a protective shell to preserve CdS but also provides abundant reactive sites and forms a type I junction, giving rise to remarkable hydrogen production activities. The optimum hydrogen production rate based on CdS@MoS2 core-shell composite reaches 26.14 mmol·h-1·g-1, which is about 54 times greater than that of pure CdS and about twice that of CdS nanowires with 1% Pt. Impressively, the presentation of MoS2 nanosheets can effectively avoid photocorrosion, which resulted in 12 h stable hydrogen production.

Defect Engineering and Phase Junction Architecture of Wide-Bandgap ZnS for Conflicting Visible Light Activity in Photocatalytic H2 Evolution.

ZnS is among the superior photocatalysts for H2 evolution, whereas the wide bandgap restricts its performance to only UV region. Herein, defect engineering and phase junction architecture from a controllable phase transformation enable ZnS to achieve the conflicting visible-light-driven activities for H2 evolution. On the basis of first-principle density functional theory calculations, electron spin resonance and photoluminescence results, etc., it is initially proposed that the regulated sulfur vacancies in wurtzite phase of ZnS play the key role of photosensitization units for charge generation in visible light and active sites for effective electron utilization. The symbiotic sphalerite-wurtzite phase junctions that dominate the charge-transfer kinetics for photoexciton separation are the indispensable configuration in the present systems. Neither ZnS samples without phase junction nor those without enough sulfur vacancies conduct visible-light photocatalytic H2 evolution, while the one with optimized phase junctions and maximum sulfur vacancies shows considerable photocatalytic activity. This work will not only contribute to the realization of visible light photocatalysis for wide-bandgap semiconductors but also broaden the vision on the design of highly efficient transition metal sulfide photocatalysts.

(1)Rational design of a charge shunt: modification upon crystal facet engineering of semiconductor photocatalysts.

Another excellent carrier shunt is artificially bridged over different exposed facets of a semiconductor, to achieve a unique architecture with superior photoactivity, which is mainly attributed to the facet-driven charge dual-selectivity-channel separation mechanism. This novel concept may break new ground in the rational modification of crystal facet engineering of a semiconductor.

Construction of teethlike homojunction BiOCl (001) nanosheets by selective etching and its high photocatalytic activity.

Teethlike homojunctions BiOCl (001) nanosheets with tunable photoresponse were constructed by selective etching with triethanolamine and allowed fast charge separation across the interfaces to facilitate photocatalysis. The unique microstructure exhibits a superior photocatalytic activity that can be ascribed to the combined interaction of the high UV/vis light harvest, high photogenerated charge separation efficiency, and the fast interfacial charge-transfer rate based on the unique homogeneous topotactic structure. We believe that the creation of this new model junction may be a great aid in the design and preparation of efficient semiconductor based photocatalysts and a new understanding of the essential relation between the junction and the photocatalytic activity.

Constructing atomic layer g-C3N4-CdS nanoheterojunctions with efficiently enhanced visible light photocatalytic activity.

Ultrathin two dimensional (2D) materials have triggered extensive interest for their exceptional properties and potential applications. Herein, atomic layer graphitic carbon nitride (g-C3N4) was obtained by a simple ultrasonic exfoliation approach, and cadmium sulfide (CdS) nanoparticles were successfully grown on these ultrathin g-C3N4 nanosheets (UCNNS) via a facile solvothermal method. The as-prepared UCNNS-CdS nanocomposite exhibits significantly enhanced photocatalytic activity for methyl orange (MO) degradation under visible light irradiation. The enhancement of the photocatalytic activity should be attributed to the well-matched band structure and intimate contact interfaces between the UCNNS and CdS, which lead to the effective transfer and separation of the photogenerated charge carriers. The mechanism for the photodegradation of MO by the composite was also investigated in this study. This study highlights the potential applications of atomic layer g-C3N4 based photocatalysts, and we hope our work may provide a new insight for the construction of photocatalysts with efficient visible light activity.

Defect self-doped TiO2 for visible light activity and direct noble metal anchoring.

A facile approach was developed for preparing defective, self-doped TiO2, which shows remarkable visible light activity in the photocatalytic degradation of RhB and hydrogen liberation from water. Moreover, noble metal was directly deposited onto the TiO2 surface via an in situ redox reaction between surficial Ti(3+) and metal salt. The lack of involvement of foreign reducing agents or stabilizers permits intimate contact between metal nanoparticles and the TiO2 substrate, which ensures the facilitated interfacial charge transfer. The strategy presented in this work may be applied to design other defect and noble metal mediated visible-light-active photocatalysts.

Solvents mediated-synthesis of BiOI photocatalysts with tunable morphologies and their visible-light driven photocatalytic performances in removing of arsenic from water.

BiOI photocatalysts with tunable morphologies from 2D laminar structure to 3D hierarchitectures have been prepared by a hydrothermal or solvothermal way using four kinds of solvents: water, ethanol, ethylene glycol and glycerol (these solvents are abbreviated as H2O, ETH, EG, and GLY hereinafter). The viscosity of the solvents plays a key role to the evolution on the morphologies and performances of BiOI samples. The BiOI synthesized in GLY exhibits excellent visible-light photocatalytic performances toward As(III), which is highly increased to that of N-TiO2. Further investigation reveals that the surface characteristics of BiOI nanosheets, the thickness of the nanosheets, and the way by which they integrate together play important roles in photocatalytic reaction process. The main active species is detected as O2(-). Considering about the practical use, the BiOI synthesized in GLY is also work under illumination of natural sunlight, and total arsenic concentration can be decreased even below 10µg/L from 1mg/L As(III) aqueous solution within 3h, which has reached the drinking water standard (0.01mg/L). Moreover, its stable performance also shows its great potential application value in the wastewater treatment.

Exciton-free, nonsensitized degradation of 2-naphthol by facet-dependent BiOCl under visible light: novel evidence of surface-state photocatalysis.

Photoreactivity for photodegradation of 2-NAP on BiOCl nanosheets with dominant exposed (010) and (001) facets is studied under visible light via an exciton-free and nonsensitized mechanism. This phenomenon cannot be explained by semiconductor theory or self-sensitized (as those involve dyes) mechanisms. The photocatalytic activities are mainly owing to the formation of the surface state, which is confirmed to be the surface complex Bi-O-C10H7. This surface complex is characterized with ultraviolet-visible diffuse reflectance spectra, Fourier transformed infrared spectroscopy, Raman scattering, X-ray photoelectron spectroscopy, and photoelectrochemical measurement. The optical absorptivity of BiOCl is shifted from the ultraviolet light toward the visible light via a charge-transfer-complex pathway. Charge transfer after the excitation of visible light induces efficient visible photocatalytic activities. The results show that single-crystalline BiOCl nanosheets exposing (010) facets exhibit higher photoactivity due to more surface complex and more terminal bismuth atoms on the surface of BiOCl (010). Our current work is expected to offer new insight into photocatalytic theory for better understandings to photocatalytic reactions and for rational design and synthesis of photocatalyst with high activity.