Quantitative Evaluation of the Carrier Separation Performance of Heterojunction Photocatalysts: The Case of g-C3N4/SrTiO3

Heterojunction photocatalysts are of great interest in the energy and environmental fields, because of their potential to significantly increase the efficiency of harvesting solar energy. Advances in design have been hampered by the continued use of only qualitative analyses. Quantitative evaluation of the carrier separation performance is urgently needed for the design and application of heterojunction photocatalysts. Taking the g-C₃N₄/SrTiO₃ heterojunction as an example, we address the conventional energy band and electronic structure issues by first-principles analysis. After interface coupling, the band edge alignment reverses from that of the respective isolated states of the heterojunction components, suggesting new ways of thinking about the catalytic mechanism of the heterojunction. More significantly, we show the carrier separation performance of heterojunction photocatalysts can be quantitatively predicted by the nonadiabatic molecular dynamics method, enabling more precisely directed research and promoting the quantified design and application of heterojunction photocatalysis, making a contribution of great scientific significance.

Cu2O/SrTi1-xCrxO3 Heterojunction Photocatalyst for the Efficient Degradation of Isopropanol under Visible Light Irradiation

A heterojunction of Cu₂O and Cr-doped SrTiO₃ (SrTi_1-xCr_xO₃) was designed for selective photocatalytic isopropanol (IPA) oxidation under visible light irradiation. The photocatalytic oxidation of IPA was measured in a fixed-bed reactor. Cr dopants can increase the light absorption and improve the activity of the catalyst. The formation of the Cu₂O/SrTi_1-xCr_xO₃ heterojunction can further broaden the absorption range of lights and dramatically increase the photocatalytic activity for selective oxidation of IPA. The 3% Cu₂O/SrTi_0.99Cr_0.01O₃ catalyst can fully convert ∼1000 ppm IPA under illumination in 2 h. The selectivity of acetone is ∼100%. The yield is 83 and 4 times higher than that using SrTiO₃ and SrTi_0.99Cr_0.01O₃ as catalysts, respectively. By measuring the ultraviolet-visible absorption spectra and Mott-Schottky plots, we obtained the band structure of the heterojunction, which shows that the conduction and valence bands of Cu₂O are higher than those of SrTi_1-xCr_xO₃, therefore facilitating the separation and transfer of photogenerated electrons and holes. In addition, electron paramagnetic resonance spectroscopy and radical trapping tests reveal that the generation of hydroxyl and superoxide leads to photocatalytic oxidation of IPA by the heterojunction photocatalyst.

Cuprous Oxide Nanoparticles: Synthesis, Characterization, and Their Application for Enhancing the Humidity-Sensing Properties of Poly(dioctylfluorene)

In this paper, we report on the synthesis—via the wet chemical precipitation route method—and thin film characteristics of inorganic semiconductor, cuprous oxide (Cu₂O) nanoparticles, for their potential application in enhancing the humidity-sensing properties of semiconducting polymer poly(9,9-dioctylfluorene) (F8). For morphological analysis of the synthesized Cu₂O nanoparticles, transmission electron microscope (TEM) and scanning electron microscope (SEM) micrographs are studied to investigate the texture, distribution, shape, and sizes of Cu₂O crystallites. The TEM image of the Cu₂O nanoparticles exhibits somewhat non-uniform distribution with almost uniform shape and size having an average particle size of ≈24 ± 2 nm. Fourier transformed infrared (FTIR) and X-ray diffraction (XRD) spectra are studied to validate the formation of Cu₂O nanoparticles. Additionally, atomic force microscopy (AFM) is performed to analyze the surface morphology of polymer-inorganic (F8-Cu₂O) nanocomposites thin film to see the grain sizes, mosaics, and average surface roughness. In order to study the enhancement in sensing properties of F8, a hybrid organic–inorganic (F8-Cu₂O) surface-type humidity sensor Ag/F8-Cu₂O/Ag is fabricated by employing F8 polymer as an active matrix layer and Cu₂O nanoparticles as a dopant. The Ag/F8-Cu₂O/Ag device is prepared by spin coating a 10:1 wt% solution of F8-Cu₂O nanocomposite on pre-patterned silver (Ag) electrodes on glass. The inter-electrode gap (≈5 μm) between Ag is developed by photolithography. To study humidity sensing, the Ag/F8-Cu₂O/Ag device is characterized by measuring its capacitance (C) as a function of relative humidity (%RH) at two different frequencies (120 Hz and 1 kHz). The device exhibits a broad humidity sensing range (27–86%RH) with shorter response time and recovery time, i.e., 9 s and 8 s, respectively. The present results show significant enhancement in the humidity-sensing properties as compared to our previously reported results of Ag/F8/Ag sensor wherein the humidity sensing range was 45–78%RH with 15 s and 7 s response and recovery times, respectively. The improvement in the humidity-sensing properties is attributed to the potential use of Cu₂O nanoparticles, which change the hydrophobicity, surface to volume ratio of Cu₂O nanoparticles, as well as modification in electron polarizability and polarity of the F8 matrix layer.

Emerging Hybrid Nanocomposite Photocatalysts for the Degradation of Antibiotics: Insights into Their Designs and Mechanisms

The raising occurrence of antibiotics in the global water bodies has received the emerging concern due to their potential threats of generating the antibiotic-resistive and genotoxic effects into humans and aquatic species. In this direction, the solar energy assisted photocatalytic technique offers a promising solution to address such emerging concern and paves ways for the complete degradation of antibiotics with the generation of less or non-toxic by-products. Particularly, the designing of hybrid photocatalyticcomposite materials has been found to show higher antibiotics degradation efficiencies. As the hybrid photocatalysts are found as the systems with ideal characteristic properties such as superior structural, surface and interfacial properties, they offer enhanced photoabsorbance, charge-separation, -transfer, redox properties, photostability and easy recovery. In this context, this review study presents an overview on the recent developments in the designing of various hybrid photocatalytic systems and their efficiency towards the degradation of various emerging antibiotic pharmaceutical contaminants in water environments.

Recent advances in photodegradation of antibiotic residues in water

Antibiotics are widely present in the environment due to their extensive and long-term use in modern medicine. The presence and dispersal of these compounds in the environment lead to the dissemination of antibiotic residues, thereby seriously threatening human and ecosystem health. Thus, the effective management of antibiotic residues in water and the practical applications of the management methods are long-term matters of contention among academics. Particularly, photocatalysis has attracted extensive interest as it enables the treatment of antibiotic residues in an eco-friendly manner. Considerable progress has been achieved in the implementation of photocatalytic treatment of antibiotic residues in the past few years. Therefore, this review provides a comprehensive overview of the recent developments on this important topic. This review primarily focuses on the application of photocatalysis as a promising solution for the efficient decomposition of antibiotic residues in water. Particular emphasis was laid on improvement and modification strategies, such as augmented light harvesting, improved charge separation, and strengthened interface interaction, all of which enable the design of powerful photocatalysts to enhance the photocatalytic removal of antibiotics.

Ferroelectric Materials: A Novel Pathway for Efficient Solar Water Splitting

Over the past few decades, solar water splitting has evolved into one of the most promising techniques for harvesting hydrogen using solar energy. Despite the high potential of this process for hydrogen production, many research groups have encountered significant challenges in the quest to achieve a high solar-to-hydrogen conversion efficiency. Recently, ferroelectric materials have attracted much attention as promising candidate materials for water splitting. These materials are among the best candidates for achieving water oxidation using solar energy. Moreover, their characteristics are changeable by atom substitute doping or the fabrication of a new complex structure. In this review, we describe solar water splitting technology via the solar-to-hydrogen conversion process. We will examine the challenges associated with this technology whereby ferroelectric materials are exploited to achieve a high solar-to-hydrogen conversion efficiency.

Visible-light-driven Ag/Bi3O4Cl nanocomposite photocatalyst with enhanced photocatalytic activity for degradation of tetracycline

In this study, a novel Ag/Bi₃O₄Cl photocatalyst has been synthesized by a facile photodeposition process. Its photocatalytic performance was evaluated from the degradation of tetracycline (TC) under visible light irradiation (λ > 420 nm). The 1.0 wt% Ag/Bi₃O₄Cl photocatalyst could significantly enhance the degradation of TC compared with pure Bi₃O₄Cl, with the degradation level reaching 94.2% in 120 minutes. The enhancement of photocatalytic activity could be attributed to the synergetic effect of the photogenerated electrons (e⁻) of Bi₃O₄Cl and the surface plasmon resonance (SPR) caused by Ag nanoparticles, which could improve the absorption capacity of visible light and facilitate the separation of photogenerated electron–hole pairs. In addition, electron spin resonance (ESR) analysis and trapping experiments demonstrated that the superoxide radicals (˙O²⁻), hydroxyl radicals (˙OH) and holes (h⁺) played crucial roles in the photocatalytic process of TC degradation. The present work provides a promising approach for the development of highly efficient photocatalysts to address current environmental pollution, energy issues and other related areas.

A novel Ag/Bi₃O₄Cl photocatalyst has been synthesized by a facile photodeposition process. The Ag/Bi₃O₄Cl photocatalyst exhibited excellent photocatalytic activity for the degradation of tetracycline.

Facile Construction of Dual p-n Junctions in CdS/Cu2O/ZnO Photoanode with Enhanced Charge Carrier Separation and Transfer Ability

With the gradually increasing demand for solving the environmental pollution problem and energy crisis, efficient photocatalysts with superior charge carrier separation and transfer ability have attracted extensive research attention. Herein, n-type CdS-decorated p-Cu₂O/n-ZnO nanorod arrays (CdS/Cu₂O/ZnO NRAs), integrating the merits of both highly ordered structure and synergistic effect derived from dual p-n junctions, were successfully fabricated and further applied to photoelectrocatalysis. In this ternary nanocomposite, fast generation, separation, and transfer of charge carriers were achieved in the Cu₂O/ZnO and Cu₂O/CdS dual p-n junction regions due to their built-in electric field and appropriate band structures. Moreover, both highly ordered ZnO NRAs and compact CdS shell play the role of an electron collector and a transport channel that efficiently consumes the photoinduced electrons in the conduction band of Cu₂O, which considerably reduces the recombination rate of charge carriers. As expected, the perfect cooperation of the three participators leads to the highest photoconversion efficiency of 2.61% at -0.275 V (versus saturated calomel electrode) and an incident photon-to-current conversion efficiency of 14.51% at 380 nm as well as the photoelectrocatalytic degradation ability of the optimized 30 min CdS/Cu₂O/ZnO NRAs photoanode as compared to that of the Cu₂O/ZnO and ZnO NRAs photoanodes. It is believed that the induced synergistic effect between dual p-n junctions and ZnO NRAs caused the superior performances of the CdS/Cu₂O/ZnO NRAs photoanode, and this ternary material with a unique structure may present a new way of thinking for potential applications in the photoelectrochemistry field.

Photoelectrochemical oxidation of ibuprofen via Cu2O-doped TiO2 nanotube arrays

A p-n junction based Cu2O-doped TiO2 nanotube arrays (Cu2O-TNAs) were synthesized and used as a working anode in a photoelectrochemical (PEC) system. The results revealed that the Cu2O-TNAs were dominated by the anatase phase and responded significantly to visible light. XPS analyses indicated that with an amount of 24.79% Cu doping into the structure, the band gap of Cu2O-TNAs was greatly reduced. SEM images revealed that the supported TiO2 nanotubes had diameters of approximately 80nm and lengths of about 2.63μm. Upon doping with Cu2O, the TiO2 nanotubes maintained their structural integrity, exhibiting no significant morphological change, favoring PEC applications. Under illumination, the photocurrent from Cu2O/TNAs was 2.4 times larger than that from TNAs, implying that doping with Cu2O significantly improved electron mobility by reducing the rate of recombination of electron-hole pairs. The EIS and Bode plot revealed that the estimated electron lifetimes, τel, of TNAs and Cu2O/TNAs were 6.91 and 26.26ms, respectively. The efficiencies of degradation of Ibuprofen by photoelectrochemical, photocatalytic (PC), electrochemical (EC) and photolytic (P) methods were measured.

Cu2O loaded titanate nanotube arrays for simultaneously photoelectrochemical ibuprofen oxidation and hydrogen generation

A p-n junction Cu2O doped TiO2 nanotube arrays (Cu2O/TNAs) were synthesized by square wave voltammetry electrochemical (SWVE) deposition method and employed as the working anode. The crystalline, optical properties, surface morphology, and structure of the Cu2O/TNAs were characterized by XRD, UV-vis absorbance edges, SEM, and XPS. Results showed that the Cu2O/TNAs were dominated by anatase phase after sintering at 450 °C with significant visible light response. XPS finding confirmed XRD results that the copper element in Cu2O/TNAs was Cu (I) instead of Cu (II). SEM images illustrated the diameter and the length of supported TiO2 nanotubes was approximately 100 nm and 2.75-4.34 μm, respectively. After Cu2O doping, the nano-tubular structure of TiO2 nanotube kept its integrity with no significant morphological change, which was beneficial for PEC applications. The photocurrent of Cu2O/TNAs was 1.45 times larger than that of TNAs, implying that Cu2O doping significantly enhanced electron mobility by reducing the recombination of electron-hole pairs. In addition, electrochemical impedance spectroscopy (EIS) measurements revealed that the recombination of photogenerated electron-hole pairs was inhibited as the bias potential was applied. Results of Bode plot further demonstrated that the electron lifetime τel of Cu2O/TNAs-20 (30.79 ms), under 0.5 V bias potential, was about 2.23 times higher than that of pure TNAs (13.82 ms). Results of electron spin resonance (ESR) analyses demonstrate that the hydroxyl radicals (OH) are responsible for the PEC decomposition of Ibuprofen.