Absorption In Visible Light Region Research Articles

Photocatalytic degradation of phenol and polycyclic aromatic hydrocarbons in water by novel acid soluble collagen-polyvinylpyrrolidone polymer embedded in Nitrogen-TiO2

Herein, we have synthesized acid-soluble collagen (ASC), polyvinylpyrrolidone (PVP), and nitrogen-doped titanium dioxide to form a novel hybrid photocatalyst nanocomposite (N-TiO2/ASC-PVP). The results of XRD, SEM and TEM revealed that the as-synthesized photocatalyst was composed of spheroidal particles, which were smaller than undoped TiO2.XPS analysis revealed that N was effectively incorporated into the lattice of TiO2 through substituting oxygen atoms, and N might coexist in the form of substitutional N (O–Ti–N) and interstitial N (TiON). The N-TiO2/ASC-PVP composite calcined at 200 and 400 °C exhibited high photocatalytic degradation rates for phenol, naphthalene (Nap), fluoranthene (Flu), phenanthrene (Phe), pyrene (Pyr), benz[a]anthracene (BaA), and anthracene (Ana), achieving a 98.6 % removal rate within 120 min at a dosage of 10 mg/L. The enhanced visible light photocatalytic activity was mainly attributed to the smaller crystal size, more surface hydroxyl groups, stronger light absorption in visible region and narrower band gap energy. This innovative hybrid photocatalyst holds immense potential for applications in materials science and nanotechnology, promising to revolutionize various industries.

Catalytic activity of Nb-doped α-Fe2O3—Heterojunction structure, ferrimagnet-like character, and high activity

Photocatalytic activity of α-Fe2O3 under visible light had been studied intensively. Rapid electron-hole recombination is the main drawback of α-Fe2O3 and the photocatalytic activity can be enhanced by transition metal doping and heterojunction structure. In the present study, α-Fe2O3 doped with various amounts of Nb were synthesized using a simple sol–gel method, and further characterization and catalytic activity were investigated. PXRD, TEM-EDS and Mössbauer measurement showed the formation of weak-ferromagnetic Nb-doped α-Fe2O3 and FeNbO4, where heterojunction structure was suggested. UV–vis spectrum showed a broad absorption in visible-light regions with a narrow band gap between 2.27 and 2.97 eV. Photo-Fenton reaction using α-Fe2O3 to decompose methylene blue (MB) was conducted to evaluate the catalytic activity. Nb-doped sample showed a significant improvement compared with pure α-Fe2O3. PXRD and Mössbauer spectroscopy revealed the α-Fe2O3 and FeNbO4 phases, which were attached to a magnet due to the ferrimagentic character of Nb-doped α-Fe2O3. The high catalytic activity with k value 7.1 * 10−2/min was obtained for 7.4Nb600. Higher catalytic activity was also observed for 20Nb600 and 40Nb600, which were driven by higher surface area, Nb substitution and heterojunction structure. Mechanistic analysis revealed that the primary reaction of MB decomposition is the Photo-Fenton process.

Enhanced photocatalytic hydrogen evolution using dual templates of sulfur-doped carbon nitride

The band structure of semiconducting photocatalysts plays a crucial role in determining their charge carrier transport characteristics and photocatalytic activity. In this work, a simple method to modulate the band structures of carbon nitride by infusing dopants and porous materials is experimentally demonstrated. A combination of trithiocyanuric acid and ammonium chloride to calcinate in an air environment, sulfur dopants and a significant amount of porosity are infused into carbon nitride concurrently. The sulfur-doped and porous carbon nitride material shows remarkable performance in photocatalytic hydrogen production, achieving a maximum hydrogen evolution rate of 4516.84 μmol g−1 h−1. Furthermore, infusion of sulfur dopants and abundant porous into carbon nitride allows for substantial and continuous tuning of the conduction and valence band positions. The band structures modulation enhanced the optical absorption in visible light region, making it suitable for efficient solar energy conversion. The findings of this work are feasible to pave a foundation for future clean energy technology.

Engineering single-atom catalysts on triazine-based covalent organic frameworks for enhanced photocatalytic performance in N2 reduction

The solar conversion of nitrogen to ammonia is a green, sustainable, and promising way to fix nitrogen. However, designing a photocatalyst with high activity, selectivity, and stability for the N2 reduction reaction (NRR) is challenging because of the slow inert activation of N2 and competitive hydrogen evolution reaction (HER). Herein, a single metal site anchored to a triazine-based covalent organic framework (Tr-COF) backbone (named TM@Tr-COF; TM = Fe, Co and Ni) is fabricated for high-performance catalytic N2 reduction. Density functional theory calculations show that the Fe@Tr-COF, Co@Tr-COF and Ni@Tr-COF can effectively activate N2 and reduce it to NH3 via the electron “acceptance–donation” process. Meanwhile, the NRR occurs via the enzymatic pathway on the Fe@Tr-COF, Co@Tr-COF and Ni@Tr-COF with a limiting potential of 0.38 V, 0.58 V and 0.54 V, respectively. Furthermore, the anchoring of Fe/Co/Ni on the Tr-COF allows the Tr-COF to be adjusted to the appropriate edge position and visible light-absorption region, indicating that the system may be a promising and efficient photocatalyst. Compared with other competitive reactions, the system exhibits high selectivity for NH3 production and inhibits competitive HERs. These findings have considerable implications for innovatively designing highly active single-atom catalysts supported by COFs.

Surface-engineered anisotropic g-C3N4 photocatalysts via green-exfoliation for visible light-driven water remediation

This study explores the modification of g-C3N4 (GCN) using extracts of betel (Piper betle) leaves and veld-grape (Cissus quadrangularis) stems. The obtained results indicate that these green extracts can effectively exfoliate the GCN-layers, modifying both the 2D structure and the 3D morphological features of GCN, leading to simultaneous chemical and physical modifications in the system. The FESEM and HRTEM images revealed the exfoliated layers with a spike-like morphology for betel extract-treated GCN (B-GCN) system, while a porous nature, along with curled layer structure, is observed in the veld extract-treated GCN (V-GCN) system. An extended absorption in visible-light region along with a reduced band gap energy is observed for V-GCN (∼2.22 eV) and B-GCN (∼2.29 eV), compared to pristine GCN (∼2.41 eV). These improvements attributed to the anisotropic morphology-induced alterations in the band structure of the systems. A notable carrier recombination resistance is also realized from the PL spectra of the treated-GCNs. The visible light-driven photocatalytic efficiencies of both the pristine and treated-GCNs in degrading methylene blue (MB), rhodamine B (RhB) and their mixture (MB+RhB) are investigated under solar irradiation. The results revealed that the V-GCN and B-GCN exhibited around 100% and over 80% degradation for MB and RhB dye, respectively. Notably, in the case of mixed dyes, the treated-GCN systems demonstrated enhanced degradation compared to pristine. This enhancement can be attributed to their improved band structure resulting from a greater layer exfoliation, morphological changes, and the presence of nitrogen defects in the modified systems. The recycling studies demonstrated that the extract-treated GCN is sable and can remain sustainable for scaled-up photocatalytic applications.

Construction of S-scheme Cs3PMo12O40/MnIn2S4 heterojunction for efficient photocatalytic removal of antibiotics: Degradation pathways, toxicity evaluation and mechanism insight

Developing highly efficient photocatalysts for the removal of antibiotics and heavy metals is of vital importance but remains a great challenge. In this investigation, a novel S-scheme Cs3PMo12O40/MnIn2S4 (CPM/MIS) heterojunction with core-shell structure was fabricated successfully via hydrothermal synthesis/dissolution-precipitation approaches, which was labelled as x CPM/MIS (x = 5, 7, 9 and 11, respectively). In the composites, these 2D MIS nanoflakes were securely and uniformly affixed on the exterior of 3D CPM nanospheres, which was verified through SEM and TEM. These as-produced materials manifested enhanced photocatalytic activity towards antibiotics (tetracycline (TC) and ciprofloxacin (CIP)) degradation and Cr(VI) reduction with visible light, and the removal rates of the optimal 9 CPM/MIS for TC, CIP and Cr(VI) could reach 97.81%, 61.78% and 67.07%, respectively. Of note, these resulting CPM/MIS composites possessed excellent stability and reusability. The outstanding photocatalytic property was attributed to the synergistic effect arising from the advantageous core-shell structure and S-scheme heterostructure. This configuration strengthened robustly interfacial interaction between the constituents, which effectively enhanced light absorption in visible region, promoted the separation and transfer efficiency of photoinduced carriers, and preserved the charge carriers with heightened redox abilities. The ESR spectra and trapping tests confirmed the dominating role of holes and superoxide radical in contaminants removal. Additionally, the high-performance liquid chromatography-mass spectrometry (HPLC-MS) technique was employed to identify the photodegradation pathways of TC. And the product toxicity was evaluated using QSAR prediction. Conclusively, combining the in situ XPS data and analysis of energy band structure, a S-scheme catalytic mechanism was elucidated. This study opens new avenues for systematically designing and fabricating S-scheme heterojunction photocatalysts with outstanding catalytic property for contaminants removal.

Preparation of PbBiO2I ultrathin nanosheets with rich oxygen vacancies for enhanced visible-light-driven photocatalytic activities

Photocatalytic oxidation technology is deemed as a prospective approach to settle the global environmental crisis. Nevertheless, the photocatalytic performance is limited by the insufficient solar light harvesting ability and disappointing charge carrier separation efficiency of photocatalysts. Herein, PbBiO2I ultrathin nanosheets with tunable oxygen vacancy (OV) concentrations were successfully fabricated via ionothermal process. The crystal structure, morphology and photoelectrochemical properties of the acquired catalysts were systematically studied. The photocatalytic degradation results demonstrate that rich oxygen vacancy (ROV) PbBiO2I possesses the highest photocatalytic degradation activity, which is about 2.9 and 35.0 times higher than those of deficient oxygen vacancy (DOV) PbBiO2I and bulk PbBiO2I in rhodamine B (RhB) degradation. The enhanced visible-light absorption region arising from bulk oxygen vacancy and surface oxygen vacancy can serve as highly active sites for catalytic reaction. This contributes to enriching electrons to accelerate oxygen molecular activation and boost charge separation. Additionally, superoxide radicals (O2•-) and holes (h+) are proved to be the major reactive species during photocatalytic process. By which, a feasible photocatalytic mechanism was primarily proposed. This research can offer a new avenue for developing bismuth-based defective photocatalyst in the field of environmental remediation.

Daul Z-scheme heterojunction BiOBr/Bi2O2.33/g-C3N4 for enhanced visible-light-driven tetracycline hydrochloride degradation

The construction of heterojunction photocatalysts with superior visible light photocatalytic performance is an effective strategy to addressing antibiotic pollution. A dual Z-scheme heterojunction BiOBr/Bi2O2.33/g-C3N4 was synthesized via hydrothermal and calcination methods, exhibiting exceptional degradation TC-HCL efficiency under visible light irradiation. The well-designed heterojunction was comprehensively supported by SEM, XPS, XRD and other series of characterization. Moreover, the BBCN50 heterojunction demonstrated an optimal degradation efficiency of 97.0% in 60 min compared to BB and CN with efficiencies of 90.8% and 70 respectively. The superior photocatalytic performance is attributed to the significantly broadened visible light absorption region and enhanced migration and separation of photogenerated electron-hole pairs facilitated by the fabricated heterojunction. Moreover, cyclic interpretation and free radical capture research have confirmed both the high stability of catalyst and its Z-type charge transfer mechanism.

Carbon Dots Modification Surface of Titanium Dioxide and Their Photocatalytic Activity

This work, we develop the efficient visible-light-responsive titanium dioxide photocatalyst using carbon dots as a sensitizer (C-dots/TiO2). C-dots was synthesized via a simple one-pot reaction by microwave-assisted pyrolysis method using orange juice as carbon precursors. C-dots/TiO2 samples were prepared by a facile route. Moreover, the micro-structure and optical properties of as-prepared C-dots/TiO2 have been evaluated using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and ultraviolet–visible diffuse reflection spectroscopy (DRS). The modification surface of TiO2 with carbon dots enhanced the light absorption in visible region. The photocatalytic properties of as-prepared pure TiO2 and C-dots/TiO2 were also explored indigo carmine decolorization under visible light. The photocatalytic results revealed that the C-dots/TiO2 exhibited higher catalytic performance than the pure TiO2 under visible light.

Novel two-dimensional square-AlAs: Direct semiconductor coupled with high electron-hole mobility ratio toward sunlight-driven water-splitting

The design of new monolayered atomic motifs always attracts enormous attention due to their interesting properties induced by unique crystal phases and promising catalytic applications in low dimensional devices. Herein, we propose a novel square-AlAs monolayer based on ab initio density functional theory calculations, whose good stability is confirmed from the perspectives of energy, dynamics, thermodynamics, and mechanics. Electronic structure calculations reveal that the newly predicted square-AlAs monolayer is a direct-gap semiconductor with a bandgap of 1.39 eV, which is sensitive to in-plane strain, meanwhile the strain induced changes in bandgap allow advantageous modulations of optical absorption in visible-light region. Unfortunately, the unfavorable hydrogen evolution reaction (HER) band edge levels make square-AlAs not suitable for photocatalytic water-splitting in spite of the appropriate bandgap, high electron-hole mobility ratio and strong visible light absorption. However, a favorable effect caused by strain engineering is revealed by the fact that the square-AlAs can meet the requirement of photocatalytic water-splitting under the suitable biaxial loading. Particularly, compared to pure AlAs, the Gibbs free energy of hydrogen adsorption indicate that Boron-doping can effectively decrease the HER overpotential. Moreover, the external potential provided by photoexcited electrons for oxygen evolution reaction (OER) is quite positive, which can serve as a free and pollution-free driving force to drive OER to proceed spontaneously for pure AlAs or reduce the OER overpotential to a very low value (0.15 V) for Boron-doped AlAs, overmatching widely used IrO2 catalyst.

Boosting the sonophotocatalytic performance of BiOCl by Eu doping: DFT and an experimental study

Bismuth oxychloride (BiOCl) has a unique layered structure and uneven charge distribution, resulting in an internal electric field under polarization, which promotes the efficient separation and migration of photogenerated carriers. BiOCl could be a candidate for sonophotocatalysts. However, the low utilization of visible light limits the application of BiOCl in photocatalysts. In this study, the photocatalytic performance of rare earth element (Nd, Sm, Eu, Er and Er)-doped BiOCl was studied by density functional theory (DFT) and experimentally to screen high-performance catalysts. The band structure, density of states, and optical properties were calculated by the DFT method to predict the photocatalytic activity of rare earth-doped BiOCl. The built-in electric field formed in Eu-doped BiOCl inhibiting electron and hole recombination can be observed. Subsequently, the activity of the photocatalyst and sonophotocatalysts was evaluated. The results show that the photocatalytic and sonophotocatalytic activity of Eu-doped BiOCl is improved, which is consistent with the theoretical prediction. Combining theoretical calculations with experiments, the sonophotocatalytic activity of Eu-doped BiOCl is enhanced, mainly due to the synergistic effect of inhibiting carrier recombination, and expansion to the visible light absorption region.

Graphitic carbon nitride modified by 5-sulfonic-8-hydroxyquinoline and Fe (III) ions as visible-light photocatalyst to efficiently reduce nitroaromatic compounds

In this study, a new graphitic carbon nitride (CN) catalyst was synthesized by combining 5-sulfonic-8-hydroxyquinoline (SQ) and Fe (III) ions. Photocatalysis reduction of nitroaromatic compounds was employed to evaluate the catalytic performance of the synthesized catalyst. Compared to the pristine CN, the optimized CN-SQ-2-Fe photocatalyst showed enhanced absorption in visible light region, which promoted photogenerated charge transfer and separation. Herein, we also developed a green and efficient photocatalysis route to convert nitrophenols (NPs) into aminophenols (APs) using CN-SQ-2-Fe photocatalyst. The visible light, separation of photogenerated charges and carrier transportation of the optimized sample CN-SQ-2-Fe were significantly improved in comparison with the pristine CN and the modified samples of CN-Fe and CN-SQ-2. Accordingly, the CN-SQ-2-Fe showed a high conversion (96%) of p-nitrophenol (p-NP) to p-aminophenol (p-AP) under visible light irradiation for 2 h and possessed high photocatalytic durability. Different NP compounds were also studied under the condition of photocatalysis reduction and demonstrated high conversion (>97%). Finally, a possible mechanism was proposed for the photocatalytic reduction of p-NP by CN-SQ-2-Fe. This work provides an effective approach to prepare graphitic carbon nitride (CN) modified by 5-sulfonic-8-hydroxyquinoline (SQ) and Fe (III) ions, which is a potential visible light driven photocatalyst for the reduction of nitrobenzene derivatives.

Fe-and-N co-doped Fe-ZIF-8-NH2(1/10) prepared by molecular-scale cages effect for highly efficient photocatalytic degradation of organic dyes

The amino and iron modified Metal-organic frameworks was successfully synthesized via a skillfully strategy and used as a photocatalyst to decompose organic dyes under visible light irradiation. Results show that 50 mg catalyst can almost degrade 100% MB within just 25 min at a wide pH (3.4–11.9) range. The kinetics constant (k) on Fe-ZIF-8-NH2(1/10) is estimated to be 0.0896 min−1, significantly higher than control samples. Meanwhile, there is little effect of various water sources on catalytic activities, and the rate reaches 97.1% (in Tap water), 88.5% (in Yangtze River water) and 78.1% (in oilfield brine with ultrahigh mineralization). Besides, the Fe-ZIF-8-NH2(1/10) exhibits high stability after 5 cyclic runs, and the ICP detects a small amount of Fe3+ (0.153 mg/L) leaching. Characterization reveals the catalyst has hierarchical porous structure, a rather homogeneous geometric topology and uniformly dispersed active sites. Based on the N 1 s spectrum of XPS, the nitrogen group is successfully loaded in amino mode. Its band gap drops sharply from 5.11 eV to 2.17 eV and the peak of PL spectra is much smaller, and the Fe-ZIF-8-NH2(1/10) possesses stronger absorption in visible light region and the response wavelength is widened to 700 nm. Further, the possible mechanism of photocatalytic degradation of pollutants is also proposed. The h+ is the most effective active species, meanwhile, •O2−, e− and •OH are both apparently participated in the photodegradation process. This study introduces valuable information for constructing high active catalysts on administration of water pollution.

Enhanced tetracycline photocatalytic degradation of FeOx/Fe-Bi2O2CO3 synthesized by one-step hydrothermal method

As an effective method to reduce the antibiotic contamination in water, photocatalysis has been widely investigated. Here, we report a preparation and tetracycline photodegradation of FeOx/Fe-Bi2O2CO3 system. The system consists of FeOx nanoparticles deposited on Fe-doped Bi2O2CO3. We used a simple one-step hydrothermal technique to successfully dope Fe into the Bi2O2CO3 lattice and simultaneously deposit FeOx. Based on experiments and calculations, it is found that incorporation of Fe in Bi2O2CO3 lattice results in a preferential growth of {001} facets, which are the active facets for photocatalytic reactions, and an increased light absorption in visible region. Additionally, FeOx nanoparticles increase light absorption and carriers’ generation via an interfacial charge transfer. Moreover, FeOx acts as cocatalyst to trap photogenerated electrons and holes, reducing the carriers’ recombination. A combination of positive effects from both Fe doping and FeOx deposition increase tetracycline photodegradation performance by two to three times compared to the pristine Bi2O2CO3. Thus, this work provides an easy-to-prepare and enhanced Bi2O2CO3 – based photocatalysts, which could benefit the future development of other materials in the field.

Replacing CC Unit with B←N Unit in Isoelectronic Conjugated Polymers for Enhanced Photocatalytic Hydrogen Evolution.

Three linear isoelectronic conjugated polymers PCC, PBC, and PBN are synthesized by Suzuki-Miyaura polycondensation for photocatalytic hydrogen (H2 )production from water. PBN presented an excellent photocatalytic hydrogen evolution rate (HER) of 223.5µmolh-1 (AQY420 =23.3%) under visible light irradiation, which is 7 times that of PBC and 31 times that of PCC. The enhanced photocatalytic activity of PBN is due to the improved charge separation and transport of photo-induced electrons/holes originating from the lower exciton binding energy (Eb ), longer fluorescence lifetime, and stronger built-in electric field, caused by the introduction of the polar B←N unit into the polymer backbone. Moreover, the extension of the visible light absorption region and the enhancement of surface catalytic ability further increase the activity of PBN. This work reveals the potential of B←N fused structures as building blocks as well as proposes a rational design strategy for achieving high photocatalytic performance.

Polyacrylic acid/polyethylene glycol hybrid antifouling interface for photoelectrochemical immunosensing of CYFRA 21-1 based on TiO2/PpIX/Ag@Cu2O composite

A photoelectrochemical (PEC) transducer based on composite TiO2/PpIX/Ag@Cu2O was prepared for the detection of CYFRA 21–1. TiO2 nanomaterials were synthesized by hydrothermal method. TiO2/PpIX/Ag@Cu2O composites were obtained by combining protoporphyrin Ⅸ (PpIX) molecules and Ag@Cu2O on TiO2. This composite material has strong absorption in visible light region and excellent photoelectric chemical properties. Ascorbic acid (AA) is a good electron donor, which can remove photogenerated holes in liquid environment to inhibit the recombination of photogenerated electrons and hole pairs, thus enhancing the photocurrent and improving its stability. The results showed that the sensor can quantitatively test CYFRA 21–1 in the range of 0.1 pg/mL∼100 ng/mL. The photoelectric chemical sensor has the advantages of high sensitivity, low detection line limit and wide linear range.

Janus monolayer SiXY (X = P, as and Sb, Y = N, P, As) for photocatalytic water splitting

We theoretically propose a types of Janus monolayers SiPN and SiXY (X = As, Sb; Y = P, As) with high stability, suitable band structures and outstanding light absorption for photocatalytic water splitting. On the basis of the first-principles calculations with the HSE06 functional and EVGW0 + BSE method, we determine that monolayer SiPN has mediocre optical absorption, appropriate STH efficiency, small electronic effective mass, and indirect band gap with value of 2.49 eV. We have also explored the anisotropy-tunable electronic and optical properties under uniaxial strain. Additionally, through replacing the surface atoms in monolayer SiPN, we have built monolayer SiAsP, SiSbP, and SiSbAs, whose band gaps are 2.35 eV, 1.88 eV, and 2.17 eV, respectively. Furthermore, we obtain that monolayer SiAsP, SiSbP, and SiSbAs have smaller effective mass, higher solar to hydrogen (STH) efficiency, as well as better optical absorption in visible-light region. Our work not only propose four Janus monolayers for expanding the instances of two-dimensional Janus semiconductors but also provide a guide for modifying mediocre 2D semiconductor photocatalysts into the high-performance one for photocatalytic water splitting.

Excellent photocatalytic degradation of rhodamine B over Bi2O3 supported on Zn-MOF nanocomposites under visible light

Abstract In this article, Bi2O3@Zn-MOF hybrid nanomaterials were synthesized by supporting Zn-based metal–organic framework (Zn-MOF) through the hydrothermal method. X-ray diffractometer, Fourier transform infrared, scanning electron microscopy, energy-dispersive X-ray, N2 physisorption, X-ray photoelectron spectroscopy, and UV-Vis were used to characterize the physical and chemical properties of Bi2O3@Zn-MOF nanomaterials. The photocatalytic activity of the as-prepared hybrid has been studied over the degradation of rhodamine B (RhB). A catalytic activity of 97.2% was achieved using Bi2O3@Zn-MOF nanocomposite with the loading of 0.18 g Bi2O3, after 90 min of exposure to visible light irradiation, and the high photocatalytic performance was mainly associated with the nanorod structures, larger pore size, and broaden visible light absorption region due to the synergistic effect of the constituting materials. Furthermore, the Bi2O3@Zn-MOF nanocomposite can be reused three times and the degradation rate of RhB was maintained at 77.9%. Thus, the Bi2O3@Zn-MOF nanocomposite can act as a potential photocatalyst for the photodegradation of organic dyes in environmental applications.

Boosted degradation of tetracycline over a novel hierarchical 2D/1D S-scheme heterojunction Bi2O4 @SnS under visible light irradiation

Highly efficient photocatalytic degradation of tetracyclines (TCs) has drawn increasing interest in the field of environmental remediation. Constructing S-scheme heterojunction is a desirable strategy for booting the photocatalytic activity of the semiconductors. Herein, rod-like Bi2O4 was decorated with SnS nanosheets with excellent light harvesting ability to construct 2D/1D hierarchical S-scheme heterojunction Bi2O4 @SnS. The photocatalytic degradation of TC over Bi2O4 @SnS was carried out under visible-light. S-scheme interfacial charge transfer mode was inferred via in-situ irradiated X-ray photoelectron spectroscopy (XPS). The optimum Bi2O4 @SnS composites 20-SSBO exhibits excellent photocatalytic activity and stability for degradation of TC in both deionized water and natural river water. Within 120 min, the degradation efficiency of tetracycline reaches 91%. The degradation rate constant of TC over 20-SSBO is 3.3 and 10.6 folds that over Bi2O4 and SnS, respectively. The significant enhancement of photocatalytic activity is mainly due to two aspects: On the one hand, the successful construction of S-scheme heterojunction between Bi2O4 and SnS not only effectively promotes the separation and transfer of photogenerated carriers but also preserves electrons with strong reduction ability and photogenerated holes with strong oxidation ability. On the other hand, the 2D/1D hierarchical core-shell structure resulted in increased specific surface area and broadened visible-light absorption region. In addition, environmental factor such as pH, typical inorganic cations and anions, and natural organic matters have less effect on the photocatalytic degradation of tetracycline. The possible photocatalytic degradation pathway of TC was proposed. The S-scheme heterojunction Bi2O4 @SnS have promising application in natural Environmental remediation.

Efficient Photodegradation of Methylene Blue using WLED with Nanosphere Graphitic Carbon Nitride Compared with its Bulk Counterpart

Herein, a simple solvothermal synthesis of graphitic carbon nitride nanosphere (g-CNN) at 180 ºC is reported. The photocatalytic activity of g-CNN was studied under an in-house developed white light emitting diode (WLED) reactor and characterized by FESEM, PXRD, FTIR, EDX, UV-visible spectroscopy and BET isotherm. The g-CNN has absorbance in visible light region and exhibits enhanced photocatalytic activity compared to bulk graphitic carbon nitride (BGCN) for photodegradation of methylene blue, which attributes to its lower surface area. The photocatalytic performance of g-CNN as function of pH of dye solution and catalyst amount were also studied. The g-CNN can be used for three repeated cycles with minimal change in photocatalytic efficiency. The solvothermal synthesis method at relative low temperature introduces terminal oxygen functionalities in g-CNN, which enhance light absorption and accelerate electron transfer results in improvement of photocatalytic efficiency of g-CNN. The results demonstrated the effectiveness of g-CNN as a photocatalyst for the treatment of water using visible light from WLED.