Reduction In Band Gap Energy Research Articles

Facile synthesis of B and P doped g-C3N4 for enhanced synergetic activity between photocatalytic water splitting and BPA degradation

A facile construction of B and P doped carbon nitride as a potential photo-catalyst for splitting water to generate hydrogen or oxygen and BPA removal under visible light. B and P doping are confirmed by a series of characterizations. As the symmetrical π-conjugated rings of g-C3N4 could be destroyed by B and P doping to enhance the visible-light absorbance and n → π∗ electronic transition to provide a new pathway for the directional separation of photoexcited electrons to boost the photocatalytic activity. Significantly, the CN-BP catalyst demonstrates excellent H2 and O2 evolution rates of 4.0 mmolH2 h−1 g−1 and 0.3 mmolO2 h−1 g−1 under visible light, which is about ∼3.8 and 21.6 times higher than that of g-C3N4, respectively. Notably, without sacrificial agent, the CN-BP could remove BPA completely by oxidation to generate 30 μmol h−1g−1 H2. Both DFT calculations and characteristic results reveal that B and P doped carbon nitride reduce band gap energy, improve light harvesting and separation rate of electron-holes carriers for upgrading the photocatalytic activity.

Temperature of photoanode for photoelectrochemical water oxidation

Solar-light-driven photoelectrochemical that can utilise water for high-performance artificial photosynthesis for low-cost green hydrogen fuel production. However, the interaction of photoanode with water is crucial to its heterogeneous water oxidation for sustainable fuel production for the replacement of fossil fuels. Here, we report experiment investigations of photoelectrode with temperature for solar energy conversion. These measurements revealed that a rise in temperature affects the catalytic generation of hydrogen in three routes, viz., minimising the required energy for water splitting, reducing bandgap energy and mitigating the resistance at the interface.

The Structural, Electronic, and Optical Characteristics of Sb2−xMxO3 (M = Cu, Ni, Zn; x = 0.25) for Optoelectronic and Allied Applications: First‐Principles Study

Herein, structural, electronic, and optical characteristics of pristine Sb2O3 and doped Sb2−xMxO3 (M = Cu, Ni, Zn; x = 0.25) for optoelectronic and allied applications are computed using Tran–Blaha modified Becke–Johnson (TB‐mBJ) approximation along with Hubbard correction. The calculated negative ground‐state energy values and absence of imaginary frequency at Gamma (point predict the dynamical and structural stability of all studied composites. The spin‐polarized electronic band structure, density of states (DOS), and 3D iso‐surface charge density analysis show reduced energy bandgap values for Sb2−xMxO3 with dopant at site B. In addition, Sb2−xNixO3 is found with minimal energy bandgap along spin‐down configuration. As regards optical response of composites, Sb2−xNixO3 offers maximum electromagnetic absorption in UV region and highest optical conductivity. Henceforth, Sb2−xNixO3 is found as most promising candidate among all studied composites for optoelectronic and allied applications.

Two Birds, One Stone: Coupling Hydrogen Production with Herbicide Degradation over Metal–Organic Framework-Derived Titanium Dioxide

Consumption of contaminated water can have detrimental effects on the health of every living organism on earth. There is, thus, a need to develop novel materials and technologies to purify water. Water is also a source of hydrogen, a clean renewable fuel that can be generated through the action of a photoactive catalyst and the earth’s abundant solar energy. Using photocatalysis, we can purify water by removing organic pollutants through the photodegradation reaction (oxidation) and produce hydrogen (H2) through the hydrogen evolution reaction (reduction). However, we can combine these two reactions in a single process to achieve an efficient photocatalytic system. Herein, we report the dual-functional photocatalysis (DFP) on herbicide-contaminated water using TiO2 polymorphs derived from the amino-functionalized metal–organic framework (MOF), MIL-125-NH2. Heteroatom TiO2 doping led to the generation of N- and N,S-doped TiO2. Of all the pristine and doped TiO2 phases synthesized, the N,S-doped anatase (NSTA) was the best dual-functional photocatalyst in degrading glyphosate (PMG) with simultaneous H2 production at a rate of 660 μmol g–1 h–1. Nuclear Magnetic Resonance studies indicate the preferential cleaving of PMG’s C–N bonds, here referred to as α and β C–N bonds, leading to the formation of glycine, formic acid, and phosphoric acid as the major degradation products. Density functional theory calculations indicate PMG’s activation through the carboxy and phosphoric acid groups on the surface of NSTA and through the phosphoric acid group on the surface of TiO2-rutile. Our results suggest that the catalytic activity of NSTA can be attributed to the templated impact of the parent MOF, owing to its porosity, redshifting of the band absorption edge toward the visible region, reduced energy bandgap, surface defects, and the presence of oxygen vacancies. The binding mode of PMG to NSTA and its degradation allowed us to test the photodegradation of other herbicides, such as glufosinate ammonium and 2,4-dichlorophenoxyacetic acid. Interestingly, our MOF-derived NSTA proved to be active in purifying water when all three herbicides were combined and produced H2 with a rate of 329 μmol g–1 h–1 simultaneously.

Bactericidal Action and Industrial Dye Degradation of Graphene Oxide and Polyacrylic Acid-Doped SnO2 Quantum Dots: In Silico Molecular Docking Study.

The present work demonstrates the systematic incorporation of different concentrations of graphene oxide (GO) into a fixed amount of polyacrylic acid (PAA)-doped SnO2 quantum dots (QDs) through a co-precipitation approach. The research aimed to evaluate the catalytic and antibacterial actions of GO/PAA-SnO2 QDs. Moreover, optical properties, surface morphologies, crystal structures, elemental compositions, and d-spacings of prepared QDs were examined. X-ray diffraction patterns revealed the tetragonal configuration of SnO2, and the crystallinity of QDs was suppressed upon dopants verified by the SAED patterns. Electronic spectra identified the blue shift by incorporating GO and PAA led to a reduction in band gap energy. Fourier transform infrared spectra showed the existence of rotational and vibrational modes associated with the functional groups during the synthesis process. A drastic increase in the catalytic efficacy of QDs was observed in the neutral medium by including dopants, indicating that GO/PAA-SnO2 is a promising catalyst. GO/PAA-SnO2 showed strong bactericidal efficacy against Escherichia coli (E. coli) at higher GO concentrations. Molecular docking studies predicted the given nanocomposites, i.e., SnO2, PAA-SnO2, and GO/PAA-SnO2, as potential inhibitors of beta-lactamaseE.coli and DNA gyraseE.coli.

Phase control and induction of visible-light photocatalytic activity in hierarchical porous structure nanocrystalline TiO2 prepared using a MOF-5-derived nanoporous carbon template

BackgroundNanocasting is a powerful method to induce unique structural and morphological characteristics. It is known that the phase, morphology, and nanostructure of TiO2 facilitate its photocatalytic performance and band gap energy. In this context, we simultaneously controlled the TiO2 phase and improved its photocatalytic activity by choosing the appropriate carbon substrate and synthesis process. MethodsIn this study, a high surface area nanoporous carbon with an extremely interconnected mesoporous network and accessible pores in terms of depth and size was derived from MOF-5. This hard template used for the synthesis of titanium oxide (TiO2) nanoparticles by nanocasting. in addition to the anatase phase, the brookite phase was successfully produced using this nanocasting approach by penetrating NaF solution to the template pores under hydrothermal conditions. Significant FindingsThe results showed that, the interconnected mesoporous network of the carbon template led to the formation of brookite and anatase TiO2 with highly developed mesoporous and macroporous structures and very high surface areas of 109 and 126 m2g−1, respectively. Furthermore, the fabricated brookite and anatase showed enhanced photocatalytic efficiency in visible light because of the increase in light harvesting ability and the reduction in band gap energy to 2.84 and 2.60 eV, respectively.

Design of BiOCl/WO3@Polyaniline Organic–Inorganic Nanocomposite Photocatalyst for the Efficient Decontamination of 2-Chlorophenol from Wastewater

Advanced photocatalysts that can utilize solar energy for water purification applications are always needed. The present article reports a facile fabrication of tungsten oxide (WO3)/bismuth oxychloride (BiOCl) immobilized on polyaniline (PAn) (BiOCl/WO3@PAn) heterojunction nanocomposite photocatalyst. The designed nanocatalyst was tested for 2-chlorophenol (2-CP) decontamination from the aquatic system. Synthesized WO3, BiOCl, and BiOCl/WO3@PAn nanocomposites were distinguished via UV-DSR, photoluminescence, SEM, TEM, XRD, and XPS analysis. The combination of PAn with WO3 and BiOCl showed a synergistic impact on the photocatalytic efficiency of the BiOCl/WO3@PAn nanocomposite. The synthesized BiOCl/WO3@PAn nanocomposite showed higher visible light absorption behavior and bandgap energy reduction than the WO3 and BiOCl. The obtained data shows that 2-CP photocatalysis by the BiOCl/WO3@PAn is controlled by degradation time, pH, and pollutant amount in the solution. The highest photocatalytic degradation of 2-CP (99.7%) was recorded at pH 5 and 25 mg/L concentration within 240 min. The photocatalysis mechanism and active radical scavenging study discovered that •O2− and •OH, were responsible for the 2-CP mineralization onto the BiOCl/WO3@PAn nanocomposite. The BiOCl/WO3@PAn nanocomposite showed enhanced decontamination properties over pristine catalysts. The reusability of the synthesized BiOCl/WO3@PAn nanocomposite was evaluated. It found that the photocatalyst could be recycled for up to four cycles for 2-CP degradation without significantly losing the photocatalytic properties. The fabricated BiOCl/WO3@PAn nanocomposite catalyst presented exceptional catalytic and recycling properties, indicating an effective method for scavenging hazardous organic contaminants under solar irradiation and green technology for wastewater purification.

Promoted visible-light-driven H2 production over hydrothermally synthesized YVO4 nanorods coupled with Pt/AgInS2 nanospheres

The curiosity of hydrogen (H2) production has become a vital substitute energy resource due to its lightweight, green, and renewability. The photocatalytic production of H2 from water over nanostructured semiconductors is a talented route. This study aims to synthesize yttrium vanadate (YVO4) nanorods by hydrothermal approach coupled with different amounts of tiny silver indium sulfide (AgInS2) nanospheres at 5.0–20.0 wt%). All samples were applied for visible-light photocatalytic evolution of H2 in a water-glycerol mixture. Physicochemical description of the prepared specimens exposes the impact of adding AgInS2 on structure, surface, and light harvesting properties. The addition of 15.0 wt% AgInS2 on YVO4's has slightly reduced the specific surface area from 170 to 160 m2 g−1, while the visible light absorbance is pointedly improved due to the significant bandgap energy reduction from 3.67 to 2.49 eV. The photogenerated H2 over 15% AgInS2/YVO4 and trace Pt deposits reached 3.344 mmol g−1h−1, which continued its recyclability for five runs at 96%. This effectual photogenerated H2 evolution is ascribed to the wide-ranged light absorbance and the efficient charge separation between AgInS2 and YVO4.

Boosted natural sunlight driven photodegradation of organic dyes using rGO anchored Pr/Cu dual-doped ZnO nanocomposite: Characterization and mechanistic insight

The advancement of sunlight-driven metal oxide semiconductor-based, highly efficient photocatalysts for removing contaminants like dyes from wastewater remained a challenge. In this work, Pr/Cu dual-doped ZnO anchored with different rGO concentrations were synthesized by simple co-precipitation and ultrasonication route. The structural, morphological, and optical characterization of prepared materials was performed with different techniques and employed for degrading diverse kinds of dyes pollutants under natural sunlight illumination. The photodegradation efficiency after 40 min sunlight illumination towards Methyl Orange (MO) was 51.00, 75.00, and 99.76% for ZnPrCuO (S1), ZnPrCuO/rGO (1:1) (S2), and ZnPrCuO/rGO (1:2) (S3), respectively. The results suggested that the introduction of Pr/Cu and rGO significantly boosted the photodegradation ability of ZnO under sunlight. Especially, S3 nanocomposite exhibited the highest photodegradation of safranin-O (SO), Rhodamine-B (RhB), and methylene blue (MB) dyes, having degradation efficiency of 65.50, 91.40, and 99.80%, respectively, in 40 min. The scavenger test results exhibited that •OH and •O2− were the foremost active species in the photodegradation process. Moreover, the reusability experiments and tracing XRD after reusing samples revealed that the S1 catalyst has excellent recyclability (6th cycle). The reduction in energy bandgap and creation of impurity energy level by Pr/Cu doping leads to inhibit carrier pair recombination and effective charge transfer/separation. These findings revealed that Pr/Cu doping and rGO have the potential to enhance the visible light response of ZnO to eliminate dyes pollutants in wastewater with energy saving.

Effective enhancement of performances on photo-assisted dye degradation using a Zn coordination polymer and its post-modified Cu/Zn bimetallic analogue under natural environments

A highly stable condensed three-dimensional framework, [Zn(2,6-ndc)(H2O)] (Zn-ndc, 2,6-ndc = naphthalene-2,6-dicarboxylate, CSD entry: MIMRAB; CCDC no: 182255), and its post-modified Cu/Zn bimetallic analogue [CuxZn1−x(2,6-ndc)(H2O)] (CuZn-ndc, x = 0.45 −0.49) showed remarkably catalytic activity to greatly improve the degradation performances of organic dyes including malachite green (MG), methylene blue (MB), and methyl orange (MO) in the presence of H2O2 without and with natural light illumination. The dye degradation over Zn-ndc and CuZn-ndc both followed the order MG > > MB > MO. In addition, CuZn-ndc displayed greater photocatalytic degradation activity compared to Zn-ndc, resulting in faster degradation rate and higher degradation efficiency. Zn-ndc and CuZn-ndc both retained the crystallinity and photocatalytic activity to degrade MG, MB, and MO dyes over five consecutive usages, implying long-term stability and reusability. Of note, pH exerted an effect on the surface charge of Zn-ndc and CuZn-ndc to decrease dye degradation performances of MB and MO but not MG as the decrease of pH. Further, CuZn-ndc had more negative charges on the surface than Zn-ndc, which provided higher affinity toward dyes and thus facilitated dye degradation. Explorations on mechanism provened that the dye degradation was a H2O2-trigged oxidative degradation process, thus more H2O2 dosage led to higher short-term degradation performances. Moreover, incorporation of Cu(II) would significantly reduce band gap energy of photo-assisted catalysts and also lead to a Cu-based photo-Fenton redox cycle, both of which would produce more hydroxyl radicals and photo-generated holes and electrons as active species. This greatly enhanced the photocatalytic activity to improve the performance of dye degradation process.

SYNTHESIS AND INVESTIGATION OF STRUCTURAL, SURFACE MORPHOLOGICAL AND OPTICAL PROPERTIES OF InSe/PMItz HYBRID HETEROJUNCTION

On a series of annealed and unannealed InSe thin films which were formerly produced by electrochemical deposition method, organic PMItz semiconductor compound was growth by physical vapour deposition (PVD) method. Structural analyses of the films carried out by X-ray diffractometry (XRD) method revealed that glass/ITO/InSe film formed in hexagonal InSe phase while glass/ITO/InSe(annealed) film formed in monoclinic In6Se7 and orthorombic In4Se3 phases. Surface analyses of the layers forming heterojunction were conducted by atomic force microscoby (AFM) and it is observed that the layers are homogenous and have different roughness values. Optical analyses of the films demonstrated that annealing of the film result with increased absorption coefficient and reduced energy band gap. Moreover, other optical parameters of the films i.e. refractive indice(n), extinction coefficient (k), real dielectric constant(Er), imaginary dielectric constant(Ei) and optical conductivity were determined and compared within 300-1000 nm range.

Degradation of Carbamazepine by HF-Free-Synthesized MIL-101(Cr)@Anatase TiO2 Composite under UV-A Irradiation: Degradation Mechanism, Wastewater Matrix Effect, and Degradation Pathway

TiO2 has been hampered by drawbacks such as rapid photoelectron and hole recombination and a wide energy band gap of 3.2 eV. In this study, MIL-101(Cr)@TiO2 was synthesised without any mineraliser (HF) as part of material modification approach to overcome those pitfalls. The composite was well characterized by XRD, FT-IR, TEM, XPS, BET, TGA, and Raman spectroscopy. Under optimal synthesis conditions, the 9.17% MIL-101(Cr)@TiO2 composite exhibited 99.9% CBZ degradation after 60 min under UV-A irradiation. This can be attributed to the delayed recombination of photo-generated h+ and e− and a reduced band gap energy of 2.9 eV. A Type II heterojunction structure was proposed for the composite using the Mulligan function of electronegativity with the calculated Ecb and Evb. Besides, trapping experiments and ESR spectroscopy confirmed O2•− as the main ROS for CBZ degradation. The effects of the operating parameters such as pH, UV intensity, composite dosage, and initial pollutant concentration were also evaluated. The scavenging effects of inorganic and organic constituents of pharmaceutical wastewater on the process were also evaluated, with HCO3−, CO32−, and THF having more significant inhibition on the overall CBZ degradation. The degradation pathways of CBZ were also proposed based on detected intermediates with the aid of LC/MS/MS. The composite illustrated reusability and stability without considerable loss in the degradation performance after repeated runs. This work builds on the development of more effective photocatalysts and provides a glimpse into applications for similar MOF heterojunction photocatalysts.

Constructing asymmetric unsaturated copper coordination in Zinc(II)/Copper(I, II)-based metal-organic framework toward productive CO2-to-methanol photocatalytic conversion from CO2-capturing solution

Copper-based catalysts show potential advantages with respect to applications in CO2 photoreduction into valuable chemicals. However, there remain great challenges to reduce band gap energy and inhibit recombination of photogenerated electron-hole pairs. Herein, we report a metal-organic framework, Zn(II)/Cu(I, II)-BTC synthesized via facile one-pot solvothermal method. Asymmetric unsaturated tetrahedral copper coordination was verified by multiple characterizations including extended X-ray absorption fine structure and electron paramagnetic resonance analyses coupled with DFT calculations. Promoted separation and transfer of photogenerated electrons and largely inhibited recombination of electron-hole pairs contribute to a productive methanol yield of 4470 μmol·g−1·h−1, which is 107% higher than that over the parent Cu-BTC. In situ diffuse reflectance infrared Fourier transform spectroscopy measurement and DFT calculation were combined to elucidate the underlying mechanism. This study provides insights into effectively tuning separation and transfer of charge within copper-based photocatalysts and highlights the role of copper coordination in valence engineering.

Simple Method to Synthesize g-C3N4 Doped Sn to Reduce Bandgap Energy (Eg)

Graphitic carbon nitride (g-C3N4) has been highlighted in its unique electronic structure with a medium bandgap, high thermal and chemical stability in the ambient environment. It is promoted as a photocatalytic material. To enhance photocatalytic properties, Sn-modified g-C3N4 was synthesized from urea and Sn powder. Firstly, urea was fired at 450-650oC in the air to synthesize g-C3N4 powder. Then such g-C3N4 powder was mixed with Sn powder for 0.1, 0.3, and 0.5 mole ratio and fired at 550oC in ambient. To investigate the phase formation and light absorption, XRD and light absorption spectrophotometers were performed, respectively. The light absorption value was used to calculate band gap energy (Eg). It was found that the XRD results of synthesized g-C3N4 were on the broad peak to narrow peak in synthesized temperatures 450-650oC. The light absorption of synthesized powder at 550oC was higher than others. Thus, synthesized powder at 550oC was chosen to mix with Sn powder. It observed that E g of Sn-modified g-C3N4 decreased depending on the amount of Sn and synthesized temperatures.

CdO-supported ZrO2 heterojunctions: facile synthesis and rapid visible-light oxidation of atrazine herbicide with superb recyclability

The advancement in ceramic oxide-based photocatalysis has got much attention recently for environmental issues. Atrazine (AZ) is one of the major used herbicides in agricultural and related industries. This work familiarizes a polymeric-assisted sol-gel preparation of high surface area zirconium oxide (ZrO2) supported with cadmium oxide nanoparticles at minor content (0.5−2.0 wt%). Exploration of the synthesized heterostructures revealed the enhancement of visible-light absorbance and reduction of bandgap energy to 2.76 eV keeping the same crystalline form and high surface area of 170 m2 g‒1. The prepared photocatalysts were used to degrade AZ in water at a concentration of 231.8 μM (50 ppm). The 1.5%-introduced CdO to ZrO2 revealed the best-performed photocatalyst for complete oxidation of AZ within 40 at an optimized dose of 1.6 g l–1. This novel ceramic photocatalyst showed a chemical and structural ability to keep 98.5% of its initial efficiency after five regenerated cycles. The construction of p–n heterojunction between the p-type ZrO2 and the n-type CdO contributed to the comprehensive photocatalytic competence toward the efficient charge separation and photooxidation process.

Enhanced photocatalytic and photoelectrochemical performance of KBiFe2O5/g-C3N4 heterojunction photocatalyst under visible light

Here we report the synthesis of graphitic carbon nitride (g-C3N4)/brownmillerite KBiFe2O5 (KBFO) based heterojunction photocatalyst. The heterojunction composite revealed rod shaped KBFO embedded on the surface of g-C3N4. The distinct phases of individual compounds are revealed through X-ray diffraction. An effective reduction in bandgap energy of KBFO/g-C3N4 (KCN) composite in comparison to pristine g-C3N4 confirmed the formation of heterojunction. Photocatalytic performance of as developed heterostructures is tested and compared by degrading common organic effluent methylene blue (MB). 25 wt% of g-C3N4 content in KBFO sample shows a remarkable improvement (92% degradation efficiency) over pure KBFO (77%) and g-C3N4 (54%). The electrode composed of 25 wt% g-C3N4 content in KBFO also reveals significant photoelectrochemical response (0.3 mA/cm2) over KBFO (1.5 μA/cm2). The improvement was attributed to an effective electron-hole separation in the heterojunction. These stable and reusable KBFO/g–C3N4 heterostructures hold promising future materials for energy and environmental applications.

Charge Compensation Mechanism and Multifunctional Properties of Bi1−xBaxFeO3 (x = 0, 0.05, 0.1) Ceramics

The charge compensation mechanism of Ba2+ ion doped BiFeO3 (BFO) has been studied here in detail. The most common problem of high leakage current of ceramic BFO was noticeably resolved by significant reduction of charge defects through Ba2+ doping. The leakage current density of Bi1-xBaxFeO3 (x = 0, 0.05, 0.1) was found to be reduced to ∼3.13 × 10−8 A cm−2 for x = 0.1 from a value of 2.26 × 10−4 A cm−2 for x = 0 at an applied field of 500 V cm−1. This reduction of leakage current was caused by the reduction of charge defects which was verified through the X-ray photoelectron spectroscopy (XPS). The dielectric and ferroelectric properties of undoped and Ba2+ doped BFO were also studied here explicitly and correlated with charge compensation mechanism. The structural and vibrational characterization proved the phase pure formation and the presence of metal-oxide bonds. The optical characterization showed the reduction in energy band gap with increased Ba2+ doping in BFO (2.18, 1.71 and 1.56 eV for x = 0, 0.05 and 0.1, respectively). Another common problem of BFO, namely low remanent magnetization, was also significantly resolved through Ba2+ doping in it and the strong antiferromagnetic BFO started showing weak ferromagnetic nature with increased doping concentration.

Facile synthesis of a TiO2-Al2O3-GnPs compound and its application in the photocatalytic degradation of Diuron

New ternary materials TiO 2 -Al 2 O 3 -GnPs (TAG) were prepared by using an innocuous sol-gel method with a slight modification for the addition of graphene nanoplatelets (GnPs), under room temperature and atmospheric pressure. The materials TiO 2 -Al 2 O 3 -GnPs were prepared with variations of concentration between 0.05 and 1 wt % of GnPs. In this study, we analyzed the physicochemical properties by X-ray diffraction (XRD) and UV-Vis spectroscopy, textural properties by N 2 physisorption, morphology by scanning and transmission electron microscopy (SEM, TEM) and a chemical species analysis was carried out by X-ray photoelectron spectroscopic (XPS). The photocatalytic activity of each material was evaluated in the degradation of a model molecule, Diuron, a carcinogenic and cytotoxic herbicide used in farm fields. To determine reaction selectivity and mineralization degree, the photocatalytic reaction was monitored by using UV-Vis spectroscopy and total organic carbon (TOC). In samples with higher GnPs’ concentration, a good enough specific surface area of up to 379 m 2 /g was observed, and reduced band gap energy (2.8 eV) with respect to TiO 2 and mixed oxide (3.2 and 3.1 eV respectively), was obtained. These resulting properties were the key indicator so that the materials could be applied as photocatalysts. In the photocatalytic activity determination, TAG-0.75 was the sample that showed the best results with respect to the mixed oxide; the highest photocatalytic conversion, the reduced average life time, and increased mineralization and reaction selectivity.

Partial magnetic ion substitution of BiFeO3 Multiferroic photocatalyst for hydrogen evolution from water splitting

BiFeO 3 as a p-type photocatalyst in BiFeO 3 –CdWO 4 p-n heterojunction was modified by partial substitution of divalent Co 2+ and Ni 2+ at Fe-site to enhance the photocatalytic performance for H 2 evolution from pure water splitting. At high impurity concentrations, XRD and Raman spectroscopy revealed a phase transition from rhombohedral to orthorhombic/tetragonal with higher crystal symmetry due to larger ionic radii of Co 2+ and Ni 2+ relative to that of Fe 3+ . The excess amount of impurities also resulted in the formation of nickel ferrite (NiFe 2 O 4 ), cobalt ferrite (CoFe 2 O 4 ), sillenite (Bi 25 FeO 40 ) and mullite (Bi 2 Fe 4 O 9 ) as secondary phases. The high resolution XPS spectra of O 1s and Fe 2p indicted that the concentration of oxygen vacancy and Fe 2+ : Fe 3+ increased with doping BiFeO 3 , which is due to the structural distortion and defection. Moreover, magnetic property of BiFeO 3 was promoted by Co and Ni doping so that the residual magnetization increased from 0.009 emu/g up to 0.061 and 0.068 emu/g by 9 mol.% doping of Ni and Co, respectively. The enhanced magnetism can be attributed to the net magnetic moment caused by different magnetic moment of Fe 3+ , Co 2+ and Ni 2+ as well as the structural defection that may be a reason for spin spiral suppression. Doping with Co and Ni led to reducing band gap energy, suppression of charge recombination, and increment of charge density and mobility. The efficiency of photocatalytic H 2 evolution increased from 268.9 μmol/h gcat by pure BFO up to 449.6 and 494.7 μmol/h gcat by 9 mol.% Ni and Co doping, respectively. • BiFeO 3 was modified by substitution of Fe 3+ with larger divalent Co 2+ and Ni 2+ . • Crystal distortion and phase transition were revealed by XRD and Raman analyses. • Magnetic property was modified as a result of crystal distortion. • Charge recombination was efficiently suppressed by Co and Ni doping. • Photocatalytic H 2 evolution was boosted by 9 mol.% Co and Ni doping.

Enhanced photocatalytic performance of TiO2 nanowires by substituting noble metal particles with reduced graphene oxide

Noble metal particles have been embedded in semiconductors to improve photocatalysis efficiently, but the high cost made this approach difficult to apply widely in industry. Herein titanium dioxide/reduced graphene oxide (TiO2/rGO) nanowires in a core-shell structure were prepared. The physicochemical properties and photocatalytic performance of the specimen were characterized in comparison with TiO2 and TiO2/Pt nanowires. The rGO layer and Pt nanoparticles increased chemical states of the components, reduced bandgap energy of the nanowires, enhanced visible light absorption, improved conductance and capacitance significantly. The methylene blue as catalyzed by TiO2/Pt and TiO2/rGO nanowires was degraded to 7.9% and 8.4% in an hour, but retained 25.7% by the TiO2 nanowires. The properties and function of TiO2/rGO nanowires were close to those of TiO2/Pt nanowires, while the rGO price was much lower than that of Pt, which was of great significance for the photocatalytic application of TiO2 heterojunction materials in industry.