First-principles calculations and experimental investigation on SnO2@ZnO heterojunction photocatalyst with enhanced photocatalytic performance

Encapsulation of Cu-modified SnO2 yolk-shell in V2O5-amalgamated wrinkled g-C3N4 lamella for boosting antibiotic photodegradation

The remarkable application of tin oxide in various domains is indebted to its photoelectronic merits. However, significant efforts to discover its photocatalytic potential were restricted through arduous challenges, which were the amelioration of light-harvesting and -utilizing. In fact, the uncommon light absorption energy has drawn veil over the brilliance of astounding oxidation potential, which is much more than that of TiO2. Herein, our attention was focused on the taking advantages of self-template structure for simultaneously enjoying the two sides of photoelectronic justification as well as the S-step system for eminent charge dissociation. In this regard, the optimized Cu-modified SnO2 yolk-shell ((5)YS-CuSnO) spheres were engineered through the copper modulation into glycerate-assisted metal-organic structure. As a result, the exceptional light-harvesting was achieved through desirable defects and oxygen vacancy resulted from Cu-doping, and also efficient light-utilization was obtained by the multi-scattering/reflection effect resulted from multi-shell configuration. After the effectual incorporation (40 wt⁒) of (5)YS-CuSnO was encapsulated into the V2O5-decorated wrinkled g-C3N4 lamella (VO-WCN), the dual S-step VO-WCN@(5)YS-CuSnO introduced unprecedented levofloxacin (LFC) decontamination performance, which was kinetically 5.2 and 30.2-times greater than of the (5)YS-CuSnO and bare SnO2 yolk-shell. The conspicuous fulfillment of nanocomposite was manifested in the LFC mineralization, pharmaceutical effluent treatment within 360 min, and successive cycling reactions. The fusion of the extraordinary architecture of YS-CuSnO with S-Step system not only initiates the facile and practical photocatalytic exploitation, but shade light on some undeveloped side of tin oxide.

Enhancing the near-infrared upconversion photocatalytic activity of ZnO/Bi3Ti2O8F:Yb3+, Er3+ by modulating the internal electric field through Z-scheme heterojunction construction

Exploring strategies to improve the near-infrared response of photocatalysts is an urgent challenge that can be overcome by utilizing upconversion (UC) luminescence to enhance photocatalysis. This paper reports the fabrication of a ZnO/Bi3Ti2O8F:Yb3+, Er3+ (ZnO/BTOFYE) Z-scheme heterojunction based on a Bi3Ti2O8F:Yb3+, Er3+ (BTOFYE) UC photocatalyst via electrostatic self-assembly. Fermi energy difference at the interface of BTOFYE and ZnO generates a strong internal electric field (IEF) in the Z-scheme heterojunction, offering a novel charge transfer mode that promotes carrier transfer and separation while retaining the strong redox capability. These results are confirmed through in situ X-ray photoelectron spectroscopy, in situ Kelvin probe force microscopy, electron spin resonance, and density functional theory calculations. In addition, the effect of the IEF on the UC luminescence process of Er3+ enhances the luminescence intensity, considerably improving the UC utilization efficiency. The optimal ZnO/BTOFYE degrades 64 % of ciprofloxacin in 120 min, which is 2.3 times more than that degraded by BTOFYE. Overall, the results of this study offer a reference for the rational development of high efficiency UC photocatalysts by generating IEF in Z-scheme heterojunctions.

Synergistic Enhancement of Carrier Migration by SnO2/ZnO@GO Heterojunction for Rapid Degradation of RhB

Organic dyes in natural waters jeopardize human health. Whether semiconductor materials can effectively degrade dyes has become a challenge for scientific research. Based on this, this study rationally prepared different nanocomposites to remove organic dyes effectively. Pure SnO2 quantum dots, ZnO nanosheets, and SnO2/ZnO (ZS) binary nanocomposites are prepared using the hydrothermal method. Subsequently, SnO2/ZnO@GO (ZSG) ternary composites containing different amounts of GO, i.e., ZSG-5, ZSG-15, and ZSG-25, are synthesized by an ultrasonic water bath method, in which ZS was coupled with GO to form Z-type heterojunctions. The ZSG-15 ternary composites exhibited excellent photocatalytic activity for the degradation of rhodamine B by simulating sunlight. The test results show that the degradation rate of ZSG-15 is about 7.6 times higher than ZnO. The increase in photocatalytic activity is attributed to the synergistic effect of SnO2 and GO to improve the separation efficiency of photogenerated carriers in ZnO. Notably, the large specific surface area of GO increases the reactive sites. Compared with binary nanocomposites, ZSG-15 broadens the response range to light while further accelerating the electron transport rate and improving the photoelectric stability.

Effective chloride ion resistance of aluminum powder through interface electric field designing

Pure aluminium (Al) powder is widely used in aerospace fields as fuel while its corrosion mechanisms and anti-corrosion strategies are not thoroughly studied. Herein, corrosion mechanisms of Al nanoparticles are revealed by density functional theory (DFT) and experiments. Moreover, by utilizing the behaviour of ions moving in the electric field, an interfacial electric field is designed to endow spherical aluminium powder (sAl) with high anti-corrosion for chloride ions (Cl-). Because TiO2 presents lower electrostatic potential than Al2O3 which is on the surface of sAl, the prepared core@shell structural material (sAl@TiO2) holds an interfacial electric field and its direction is from TiO2 to Al2O3. The electric field repels the Cl- adsorption on the surface of sAl@TiO2, bringing about superior Cl- anti-corrosion.

Designing advanced S-scheme CdS QDs/La-Bi2WO6 photocatalysts for efficient degradation of RhB

Finding effective strategies to design efficient photocatalysts and decompose refractory organic compounds in wastewater is a challenging problem. Herein, by coupling element doping and constructing heterostructures, S-scheme CdS QDs/La-Bi2WO6 (CS/LBWO) photocatalysts are designed and synthesized by a simple hydrothermal method. As a result, the RhB degradation efficiency of the optimized 5% CS/LBWO reached 99% within 70 min of illumination with excellent stability and recyclability. CS/LBWO shows improvement in the adsorption range of visible light and promotes electron-hole pair generation/migration/separation, attributing the superior degradation performance. The degradation RhB mechanism is proposed by a free radical capture experiment, electron paramagnetic resonance, and high-performance liquid chromatography-mass spectrometry results, indicating that h+ and •O2 - play a significant role during four degradation processes: de-ethylation, chromophore cleavage, ring opening, and mineralization. Based on in situ irradiated X-ray photoelectron spectroscopy, Mulliken electronegativity theory, and the work function results, the S-scheme heterojunction of CS/LBWO promotes the transfer of photogenerated electron-hole pairs and promotes the generation of reactive radicals. This work not only reports that 5% CS/LBWO is a promising photocatalyst for degradation experiments but also provides an approach to design advanced photocatalysts by coupling element doping and constructing heterostructures.

Synthesis and characterization of TiO2/ZnO heterostructural composite for ultraviolet photocatalytic degrading DOM in landfill leachate

In order to investigate the photocatalytic degradation of dissolved organic matter (DOM) in landfill leachate, TiO₂/ZnO heterostructural composite powders were fabricated combining with hydrothermal synthesis and solid-state reaction method. The prepared TiO₂/ZnO composite powders consist of anatase TiO₂ nanoparticles distributing on the surface of wurtzite ZnO particles. The optical band gap of TiO₂/ZnO powder is less than that of pure ZnO or TiO₂ powder. TiO₂/ZnO catalyzers show high ultraviolet-degradation efficiency for methylene blue and dissolved organic matter. The degradation rate of TiO₂/ZnO powder for fulvic acid-like substances in landfill leachate is 2.99 times that of pure ZnO powder, and is 1.30 times that of pure TiO₂ powder. The degradation of fulvic acid-like substances by TiO₂/ZnO photocatalyst reduced some molecular weight of benzene ring structure substances in leachate. The effective separation of electron and hole in heterostructural TiO₂/ZnO photocatalyst is the main reason for its high photocatalytic degradation efficiency of DOM in landfill leachate.

Enhanced photocatalytic and antibacterial activities of S-scheme SnO2/Red phosphorus photocatalyst under visible light

The construction of wide bandgap semiconductors with heterojunctions is an effective strategy to improve the photocatalytic activity of narrow-bandgap semiconductors, such as red phosphorus (RP). The novel step-scheme (S-scheme) heterojunction can separate photocarriers effectively while retaining the high reduction-oxidation capacity of the catalyst. Herein, a SnO₂/hydrothermally treated RP (SnO₂/HRP) S-scheme heterojunction was constructed and was found to display superior performance in the photocatalytic degradation of pollutants and the disinfection of bacteria. The 5%SnO₂/HRP (mass ration of SnO₂ with 5 wt%) composite had the strongest photocatalytic activity. It could degrade 97.5% of Rhodamine B (RhB) after 12 min of light exposure. The photodegradation rate constant of this composite reached 2.96 × 10^-1 min^-1, which was 4.4 and 59.2 times higher than that of pure HRP and SnO₂, respectively. Furthermore, this S-scheme heterojunction composite exhibited a higher efficient photocatalytic antibacterial rate (99.4%) for Escherichia coli (E. coli) under visible-light irradiation, than pure HRP (66.4%) and SnO₂ (72.9%). Further mechanistic investigations illustrated that the intimate contact between HRP and SnO₂ in the S-scheme system heterojunction could effectively boost carrier transfer and improve the photocatalytic activity of the semiconductor. This investigation provided an efficient recyclable S-scheme heterojunction composite for the photocatalytic degradation of pollutants and bacteria.

Band alignment of ZnO-based nanorod arrays for enhanced visible light photocatalytic performance

A ternary semiconductor ZnO/MoS₂/Ag₂S nanorod array in an intimate core–shell structure was synthesized on glass substrates. The physicochemical properties and photocatalytical performance of the specimen were characterized and compared with single ZnO and binary ZnO/Ag₂S and ZnO/MoS₂ nanorod arrays. It is found that the coating layers depressed the band edge emission of the ZnO core, improved light absorption in the visible range, reduced charge transfer resistance, and increased photocatalytic activity. The ternary heterojunction nanorod array possessed full solar absorption with an efficiency of 52.88% for the degradation of methylene blue under visible light in 30 min. The efficiency was higher than other arrays and was 7.6 times that of the ZnO array. Theory analysis revealed that the coating layer brought different band alignment in the heterojunctions for efficient charge separation and conduction, which was beneficial for the photocatalytic performance.

The ternary ZnO/MoS₂/Ag₂S nanorod array in a core–shell structure brings different band alignments at the interfacial heterojunctions to achieve full solar absorption with efficient charge separation and conduction and photocatalytic performance.

Magnetically separable type-II semiconductor based ZnO/MoO3 photocatalyst: a proficient system for heteroarenes arylation and rhodamine B degradation under visible light

Shedding light on a magnetically retrievable ZnO/MoO3 photocatalyst that efficiently coupled diazonium substituted arenes with heteroarene substrates along with efficient degradation of toxic Rhodamine B.

Sonochemical synthesis of ZnCo2O4/Ag3PO4 heterojunction photocatalysts for the degradation of organic pollutants and pathogens: a combined experimental and computational study

ZnCo2O4/Ag3PO4 heterostructure nanoparticles were prepared by a facile ultrasonic method and characterized by various techniques. The photocatalytic activity of ZnCo2O4/Ag3PO4 nanoparticles was investigated for the degradation of organic pollutants (methyl...

Synthesis of Cu3P/SnO2 composites for degradation of tetracycline hydrochloride in wastewater

Antibiotic drugs have become dominating organic pollutants in water resources, and efficient removal of antibiotic drugs is the priority task to protect the water environment. Cu₃P/SnO₂ photocatalysts of various Cu₃P loadings (10-40 wt% Cu₃P) were synthesized using a combination of hydrothermal synthesis and a partial annealing method. Their photocatalytic activity was tested for tetracycline hydrochloride (TC-HCl) degradation under visible light irradiation. Cu₃P/SnO₂ samples were characterized by X-ray diffraction (XRD), N₂-adsorption, ultraviolet-visible diffuse reflectance spectra (UV-vis DRS), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The results showed that the p-n type heterostructure between Cu₃P and SnO₂ was successfully constructed, and addition of Cu₃P to SnO₂ could improve its photocatalytic activity at an optimized loading of 30 wt% Cu₃P. In photocatalytic degradation studies, removal rates of around 80% were found in 30 minutes of dark reaction and 140 min of photodegradation. The removal rate was superior to that of Cu₃P and SnO₂ alone under the same experimental conditions. According to trapping experiments and electron spin resonance (ESR) measurements, photogenerated holes (h⁺) and superoxide radicals ˙O₂ ^- were considered as the main oxidation species in the present system. Finally, the reuse experiments showed high stability of Cu₃P/SnO₂. This study reports Cu₃P as a cocatalyst combined with semiconductor SnO₂ to form a highly efficient heterogeneous photocatalyst for the degradation of tetracycline hydrochloride for the first time.

Water hyacinth plant extract mediated green synthesis of Cr2O3/ZnO composite photocatalyst for the degradation of organic dye

The Cr2O3/ZnO composite catalysts with varying the amount of chromium precursors abbreviated as 0.02CrZn, 0.04CrZn, 0.06CrZn, 0.08CrZn, 0.1CrZn, and fixed the amount of Zn precursor (0.1 M) were prepared by using water hyacinth (Eichhornia crassipes) extract as a template/capping agent. The prepared catalysts were characterized and the catalytic performances of the catalysts were also checked for the degradation of methylene blue (MB) dye. The photocatalytic MB dye degradation by 0.08CrZn catalyst was achieved and 85% of MB dye was degraded within 90 min irradiation time. However, 0.1CrZ, 0.06CrZ, 0.04CrZ, 0.02CrZ, ZnO, and Cr2O3 catalysts degrade only 80, 74, 79, 76, 52, and 74% of MB dye, respectively. The catalytic performances indicated that the addition of optimum amount of chromium precursor in the preparation of Cr2O3/ZnO composite catalysts with the aid of Eichhornia crassipes plant extract enhances the catalytic activities. This performance enhancement could be as a result of reducing the electron/hole pair separation and the porosity resulted from the plant extract in the catalyst system.

Photocatalytic Activity of Cu2S/WO3 and Cu2S/SnO2 Heterostructures for Indoor Air Treatment

Volatile organic compounds (VOCs) are commonly found in indoor spaces (e.g., homes or offices) and are often related to various illnesses, some of them with carcinogenic potential. The origins of VOC release in the indoor environment are in office products, building materials, electronics, cleaning products, furniture, and maintenance products. VOC removal can be done based on two types of technologies: adsorption in specific materials and decomposition via oxidative processes. The present article reports the development and photocatalytic activity of two heterostructures (Cu2S/WO3 and Cu2S/SnO2) used for indoor air decontamination. The acetaldehyde removal rate is discussed in correlation with the S-scheme mechanisms established between the heterostructure components but also comparatively with the bare catalysts' activity. Acetaldehyde was considered as a VOC reference because it was found by the International Agency for Research on Cancer to be one of the most frequent air toxins with potential carcinogenic effects. The samples contained monoclinic WO3, tetragonal SnO2, and orthorhombic Cu2S crystalline structures. The Cu2S crystallite size in the heterostructure varied from 75.9 to 82.4 Å, depending on the metal oxide substrate. The highest photocatalytic efficiency (75.7%) corresponded to Cu2S/SnO2, with a constant rate of 0.106 s-1 (which was three times faster than WO3 or SnO2 and seven and a half times faster than Cu2S).

Extra Li-Ion Storage and Rapid Li-Ion Transfer of a Graphene Quantum Dot Tiling Hollow Porous SiO2 Anode

Graphene is widely used to enhance the electrochemical performance of anodes. However, graphene tends to be vertical with the lithium-ion (Li⁺) diffusion direction, and a few heterointerfaces are formed between graphene and active materials by point-to-point contact. Herein, a graphene quantum dots (GDs) tiling hollow porous SiO₂ (HSiO₂@GDs) anode is predicted by density functional theory (DFT) and is achieved by experiments. Due to the ultrasmall size, the tiling of GDs would provide Li⁺ a rapid diffusion channel and abundant heterointerfaces (face-to-face contact) between the GDs and the hollow porous SiO₂ (HSiO₂). Moreover, owing to the higher electrostatic potential of SiO₂, the large-scale local electrical field from GDs to HSiO₂ is established at the heterointerfaces, which provide extra Li⁺ storage sites and further facilitate the Li⁺ transfer. To our knowledge, the HSiO₂@GDs shows the highest specific capacities at various current densities (such as ∼1100 mA h/g at 5 A/g and ∼2250 mA h/g at 0.2 A/g) among reported silicon oxides anodes and presents excellent cycling stability (∼1000 mA h/g after 2000 cycles at 3 A/g). Moreover, the design idea is available to design other widely studied graphene-containing anodes such as the Si, SnO₂, TiO₂, and MoS₂.

Sputtered SnO2/ZnO Heterostructures for Improved NO2 Gas Sensing Properties

A highly sensitive and selective NO2 gas sensor dependent on SnO2/ZnO heterostructures was fabricated using a sputtering process. The SnO2/ZnO heterostructure thin film samples were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Sensors fabricated with heterostructures attained higher gas response (S = 66.9) and quicker response-recovery (20 s, 45 s) characteristics at 100 °C operating temperature towards 100 ppm NO2 gas efficiently in comparison to sensors based on their mono-counterparts. The selectivity and stability of SnO2/ZnO heterostructures were studied. The more desirable sensing mechanism of SnO2/ZnO heterostructures towards NO2 was described in detail.

First-Principles Calculations of the Electronic Structure and Optical Properties of Yttrium-Doped ZnO Monolayer with Vacancy

The electronic structures and optical characteristics of yttrium (Y)-doped ZnO monolayers (MLs) with vacancy (zinc vacancy, oxygen vacancy) were investigated by the first-principles density functional theory. Calculations were performed with the GGA+U (generalized gradient approximation plus U) approach, which can accurately estimate the energy of strong correlation semiconductors. The results show that the formation energy values of Y-doped ZnO MLs with zinc or oxygen vacancy (V_Zn, V_O) are positive, implying that the systems are unstable. The bandgap of Y-V_Zn-ZnO was 3.23 eV, whereas that of Y-V_O-ZnO was 2.24 eV, which are smaller than the bandgaps of pure ZnO ML and Y-doped ZnO MLs with or without V_O. Impurity levels appeared in the forbidden band of ZnO MLs with Y and vacancy. Furthermore, Y-V_Zn-ZnO will result in a red-shift of the absorption edge. Compared with the pure ZnO ML, ZnO MLs with one defect (Y, V_Zn or V_O), and Y-V_Zn-ZnO, the absorption coefficient of Y-V_O-ZnO was significantly enhanced in the visible light region. These findings demonstrate that Y-V_O-ZnO would have great application potential in photocatalysis.

Facile one-pot synthesis of heterostructure SnO2/ZnO photocatalyst for enhanced photocatalytic degradation of organic dye

In this work, heterostructure SnO₂/ZnO nanocomposite photocatalyst was prepared by a straightforward one step polyol method.