Vis DRS Spectroscopy Research Articles

One-step in situ green template mediated porous graphitic carbon nitride for efficient visible light photocatalytic activity

We report a facile and sustainable route to prepare the porous g-C3N4 by using starch as green in situ gaseous template and melamine as a precursor. The as-prepared g-C3N4 exhibited a porous thin sheet like structure with a larger surface area and showed an efficient separation efficiency for radiative charge carriers. The textural structure and morphology of the porous g-C3N4 materials were well characterized by TEM, SEM, XRD, BET, FT-IR, Raman, XPS, UV–vis DRS and PL spectroscopy. The starch mediated porous g-C3N4 photocatalyst demonstrated significantly an enhanced visible light photocatalytic performance and excellent physicochemical stability for the photodegradation of organic pollutants (including rhodamine B and phenol). The results revealed that, the optimized gaseous template contents had a significant influence on photooxidative chemical reaction of the as-prepared samples. The radical scavenging experiments proved that holes and O2− are the main reactive species responsible for the visible light degradation of rhodamine B. This simple, economical and green strategy using starch as gaseous porogen agent for the fabrication of porous g-C3N4 with excellent visible-light photocatalytic activity is desirable for environmental remediation and solar energy applications.

Synthesis, characterization and photocatalytic activity of pure and Zn-doped In2O3 nanostructures

In this work, pure and Zn-doped In2O3 nanostructures had been synthesized by facile template-free hydrothermal method. Structural, morphological and optical properties were characterized by using XRD, FT-IR, HR-SEM and HR-TEM, EDS, XPS, UV-DRS and PL measurement techniques. X-Ray Diffraction analysis showed that the prepared nanostructures were of pure cubic phase and the crystallite size was decreased with increased Zn dopant. HR-SEM and HR-TEM analysis showed morphological transformation with good crystallanity and decrease of particle size with doping. XPS spectra were recorded to reveal the composition and elemental state of Zn-doped In2O3. The optical properties of synthesized nanostructures were analyzed with UV–Vis DRS spectroscopy and band gap was found to decrease from 3.5 to 3.38 eV with Zn dopant concentration. The photoluminescence spectra displayed orange emission peaks at 600 nm for all prepared nanostructures. Photodegradation of Methylene Blue (MB) dye under ultra violet light radiation was studied with synthesized nanostructures.

G-C3N4/(Cu/TiO2) nanocomposite for enhanced photoreduction of CO2 to CH3OH and HCOOH under UV/visible light

Cu-modified graphitic carbon nitride (g-C3N4) and titanium dioxide (TiO2) nanocomposites for enhanced photocatalytic CO2 reduction with H2O under UV and visible light irradiations have been investigated. The photocatalysts, prepared by pyrolysis and impregnation were characterized by XRD, FE-SEM, TEM, FT-IR, N2 adsorption-desorption, XPS, UV–vis DRS and PL spectroscopy. The Cu-metal loaded over TiO2 and g-C3N4 enhanced CO2 reduction efficiency to CH3OH and HCOOH by fostering carrier charge separation. The Cu-metal in the composite as well as the wt.% ratio of g-C3N4 and TiO2 also influenced the photoactivity and products selectivity. The low band gap, electronic structure and visible light absorption capacity of g-C3N4 facilitated the transfer of photo-generated electrons to Cu/TiO2 in the composite. Moreover, the position of the metal in the composite affected the electrons distribution and hence enhanced the photoactivity. The maximum yield of the products detected under visible light were 2574 and 5069μmol/g.cat of CH3OH and HCOOH, respectively. The yield of CH3OH under visible light was four fold higher compared to UV-light irradiation. The ratio (30:70) of g-C3N4 and Cu/TiO2 in the composite and the use of visible light improved the efficiency of the photocatalytic system. The stability of the photocatalyst prevailed in continuous CH3OH production under visible light irradiation compared to UV-light in cyclic runs. Possible reaction mechanisms were proposed to understand the movement of electrons and holes and the function of both UV and visible light for CO2 reduction over the g-C3N4/TiO2 (30:70) photocatalyst.

Preparation and characterization of sol-gel derived Ce4 + doped hydroxyapatite and its in vitro biological evaluations for orthopedic applications

For the first time, in the present investigation, we have attempted the refluxing based sol-gel technique to synthesize cerium (Ce4+) doped hydroxyapatite (Ce-HAP) with different concentrations such as 0.5, 0.75, 1 and 1.25%. The Ce-HAP powders were evaluated for in vitro biological studies such as hemocompatibility, antibacterial activity and biocompatibility. These in vitro studies have demonstrated the prominent results such as compatible nature with human blood (<5% hemolytic ratio) and excellent pathogen inhibition efficiency towards Escherichia coli (E. coli), Pseudomonas aeruginosa (P. aeruginosa), Staphylococcus aureus (S. aureus) and Bacillus subtilis (B. subtilis) respectively. Among these, E. coli shows more susceptible towards 0.5–1.25% of Ce-HAP. In vitro biocompatibility study was performed on the 1.25% of Ce-HAP using MG-63 cells at various concentrations of 200–1000μg/ml for 24–48h. It was found that 1.25% of Ce-HAP powder was non-toxic up to the level of 600μg/ml concentrations towards MG-63 cells with regular cell attachment and proliferation. The Ce-HAP materials were further characterized by UV–vis DRS spectroscopy, ATR-FTIR, Powder-XRD, SEM-EDAX, TEM, ICP-OES and XPS analysis. Therefore, this study proves that the developed Ce4+ doped HAP can be widely used in orthopedic and dentistry field with improved biological properties.

Novel N/Bi-BiOCl nanoplates synthesised in NH3 atmosphere and their enhanced photocatalytic activity

Novel N-doped Bi-BiOCl nanoplates with the diameter of 50–200 nm were successfully fabricated via calcination route under NH3 atmosphere. The obtained products were investigated by N2 physical adsorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–vis DRS and X-ray photoelectron spectroscopy. The characterisations results showed that at appropriate temperatures (300–400 °C), N can be doped into BiOCl and part of Bi3+ can be reduced to Bi metal phase. N-doping or simultaneous Bi deposition can effectively extend the light absorption of BiOCl from UV (200 nm) range to near-infrared region. Under simulated solar light irradiation, the optimal N-doped Bi-BiOCl nanoplates displayed 1.5 times of activity of the pure BiOCl.

Effects of first-row transition metals and impregnation ratios on the physicochemical properties of microwave-assisted activated carbons from wood biomass

First-row transition metals (Co, Ni, Cu and Zn) were successfully used in the preparation of activated carbons from wood biomass via microwave-assisted irradiation. Physical-chemical properties of the produced materials (MWAC) were studied by nitrogen adsorption–desorption curves, SEM, FTIR, UV–vis DRS and synchronous fluorescence spectroscopy, CHN elemental analysis, TGA/DTG, pHzpc, hydrophobic properties, and total acidity and basicity groups. Results showed that the metals were bound successfully in different amounts with surface functional groups of the wood biomass through ion exchange and surface complexation interaction during the impregnation step. Zn2+ and Cu2+ formed the most complexes. MWAC impregnated with Zn2+ showed higher pore volumes and surface areas, followed by Cu2+, Co2+ and Ni2+, independently of the ratio used. As the metal : biomass ratio was increased from 0.5 to 2, the surface area of MWAC increased from 300 to 620m2g−1 for Co-MC, 260 to 381m2g−1 for Ni-MC, 449 to 765m2g−1 for Cu-MC and from 572 to 1780m2g−1 for Zn-MC. The samples showed high values of carbon contents and oxygen-containing groups. An adsorption experiment revealed that samples prepared using ZnCl2 showed the highest sorption capacities (qe) for the tested adsorbates, followed by CuCl2, CoCl2 and NiCl2. These results matched with the surface areas and pore volumes trends, which were found to follow atomic number and melting point trends–Ni(II)<Co(II)<Cu(II)<Zn(II), rather than the Irving-Williams Series. The sorption capacities (qe) of molecules followed this order: 2-nitro phenol>bisphenol A>hydroquinone>4-nitro phenol>2-naphtol>paracetamol>caffeine>resorcinol.

Single-Site VOx Moieties Generated on Silica by Surface Organometallic Chemistry: A Way To Enhance the Catalytic Activity in the Oxidative Dehydrogenation of Propane

We report here an accurate surface organometallic chemistry (SOMC) approach to propane oxidative dehydrogenation (ODH) using a μ2-oxo-bridged, bimetallic [V2O4(acac)2] (1) (acac = acetylacetonate anion) complex as a precursor. The identity and the nuclearity of the product of grafting and of the subsequent oxidative treatment have been systematically studied by means of FT-IR, Raman, solid-state (SS) NMR, UV–vis DRS, EPR and EXAFS spectroscopies. We show that the grafting of 1 on the silica surface under a rigorous SOMC protocol and the subsequent oxidative thermal treatment lead exclusively to well-defined and isolated monovanadate species. The resulting material has been tested for the oxidative dehydrogenation of propane in a moderate temperature range (400–525 °C) and compared with that of silica-supported vanadium catalysts prepared by the standard impregnation technique. The experimental results show that the catalytic activity in propane ODH is strongly upgraded by the degree of isolation of the VO...

Effects of the molar ratio on the photo-generated charge separation behaviors and photocatalytic activities of (BiO)2CO3-BiOBr composites

The molar ratio of two semiconductors will remarkably influence the photo-induced charge separation behaviors of the composites constructed, thus affecting the corresponding photocatalytic activity. Therefore, it is critical to reveal the relationship between the molar ratio of two semiconductors and the photo-induced charge separation; the information can shed light on the study of nature of surface catalysis. In this work, (BiO)2CO3-BiOBr composites were facilely fabricated in-situ through a pore impregnating approach using HBr aqueous solution. The samples were studied by BET, XRD, SEM, UV–Vis DRS and surface photovoltage spectroscopy (SPS). The photocatalytic activities of the samples were evaluated by the discoloration of methyl orange (MO) aqueous solution upon the simulated sunlight illumination. The results reveal that the (BiO)2CO3-BiOBr composite with 3/4 M ratio of (BiO)2CO3/BiOBr displays the highest photo-induced charge separation rate and photocatalytic activity, the results further manifest that no different electronic transfer property occurs after coupling (BiO)2CO3 with BiOBr.

Fabrication of highly active Melem/Zn0.25Cd0.75S composites for the degradation of bisphenol A and methyl orange under visible light irradiation

Metal-free polymeric catalyst hold great promise owing to their abundant sources, low-cost fabrication and easy processibility. Melem, an important intermediate during condensation of melamine rings to graphitic carbon nitride (g-C3N4), was synthesized by simple solid phase polymerization process. A novel Melem/Zn0.25Cd0.75S composite was fabricated through a facile one-step hydrothermal method. The as-products were characterized by X-ray diffraction (XRD), UV–vis DRS spectroscopy, fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM). The TEM and HRTEM results reveal that Zn0.25Cd0.75S nanoparticles and Melem closely contact with each other to form an intimate interface. The as-prepared composites exhibit significantly enhanced visible light photocatalytic performance for the degradation of Methyl orange (MO) and Bisphenol A (BPA), which could be attributed to the effective photo-induced charges transfer and separation in Melem/Zn0.25Cd0.75S composites. On the basis of radical scavenger experiments, superoxide radicals and holes are suggested to play a critical role in MO degradation over Melem/Zn0.25Cd0.75S heterojunctions. A possible mechanism for charge separation and transfer in the Melem/Zn0.25Cd0.75S composites was proposed to explain the enhanced photocatalytic performance.

Phase composition, structural peculiarities and catalytic properties of supported MgO-V2O5/Al2O3 catalysts for oxidative dehydrogenation of propane: Insight into formation of surface Mg-V-O phase

MgO-V2O5/Al2O3 catalysts for oxidative dehydrogenation of propane are prepared by a consecutive or one-step impregnation of γ-Al2O3 with V and/or Mg precursors. The formed γ-Al2O3-supported surface Mg-V-O phases are characterized by XRD, Raman, UV–vis DR spectroscopy, H2-TPR and zeta potential measurements. The synthetic approaches are shown to strongly affect the phase composition and catalyst surface structure, which determine the catalytic properties of the materials under consideration.

A comparative study on adsorption and photocatalytic dye degradation under visible light irradiation by mesoporous MnO2 modified MCM-41 nanocomposite

In situ incorporation of semiconducting mesoporous MnO2 (meso-MnO2) into the MCM-41 generates a high surface area meso-MnO2–MCM-41 nanocomposite. The structural, morphological, optical and electronic properties of these catalysts were characterized by low angle and broad angle X-ray diffraction (LXRD and BXRD), X-ray photoelectron spectroscopy (XPS), UV–vis DRS spectroscopy and high resolution transmission electron microscopy (HRTEM). The incorporation of meso-MnO2 into MCM-41 through the silanol group forming nanocomposite has been evidenced from FTIR study and 29Si CP–MAS NMR spectra. Among all the catalysts, meso-MnO2–MCM-41(10) showed the highest surface area (1313 m2 g−1), narrow pore diameter (2.04 nm) and high pore volume (0.86 cm3 g−1). The activity of meso-MnO2–MCM-41 samples were compared towards adsorption and degradation of various cationic dyes such as Rhodamine 6G (Rd 6G), Methylene blue (MB), Malachite green (MG) and Rhodamine B (Rd B). The meso-MnO2–MCM-41(10) composite exhibited 100% photo degradation and adsorption activity towards 100 ppm dye solution in 60 min and 90 min, respectively. The high surface area, narrow pore diameter, high pore volume, intra-particle mesoporosity are responsible for high adsorption. Furthermore, the electron transfer and generation of OH radicals are responsible for the enhancement of photo degradation process.

Production of hydrogen from glucose by LaFeO3 based photocatalytic process during water treatment

In this work the hydrogen production from photocatalytic degradation of glucose aqueous solution using LaFeO3 catalysts was investigated under UV or visible light irradiation by light-emitting diodes (LEDs). Different LaFeO3 catalysts were prepared by solution combustion synthesis, starting from lanthanum nitrate and iron nitrate aqueous solution, and different amounts of citric acid as organic fuel. The influence of light irradiation and amount of citric acid was evaluated. The photocatalysts were characterized by different techniques, such as XRD, BET, UV–Vis DRS and Raman spectroscopy. As the amount of citric acid was increased from 0.86 to 2.15 g, the specific surface area of perovskite was increased from 4 to 24 m2/g, with crystallite size of 38 and 6 nm, respectively. Moreover, the different amounts of citric acid induced changes in the crystallinity degree of LaFeO3 perovskite. LaFeO3 catalyst prepared with a double amount of citric acid (1.72 g) compared to the initial content (0.86 g), was the most active in the photocatalytic production of H2 (up to 1.6 mmol/gcat after 4 h of UV irradiation, corresponding to 16% of hydrogen yield). With this photocatalyst the simultaneous degradation of glucose was 73% after 4 h of UV irradiation. These results are encouraging with respect to the possibility to produce hydrogen during photocatalytic treatment of sugar-containing water by using photocatalysts in the absence of noble metals.

Synthesis of cysteine, cobalt and copper-doped TiO2 nanophotocatalysts with excellent visible-light-induced photocatalytic activity

Charge separation is a vital process in order to achieve high performance TiO2-based photocatalysts. In the current study, to enhance the charge separation and suppress the charge recombination, novel nanocomposites of metal (Co and Cu) and nonmetal (C, N, S) doped TiO2 nanophotocatalyst (labeled as Co@C,N,S-doped TiO2 and Cu@C,N,S-doped TiO2) were synthesized via photochemical deposition-assisted sol–gel technique. The crystalline structures and characteristic of the prepared catalysts were analyzed by XRD, SEM, TEM, EDAX, PL, and UV–vis DRS spectroscopies. The photocatalytic performance of the samples was tested through decomposition of methyl orange (MO) aqueous solutions under UV and visible light irradiation. It was found that photodeposition of metals onto TiO2 slowed charge recombination compared to pure TiO2 in addition to formation of higher concentration of OH radicals on the TiO2 photocatalyst surface during light irradiation compared to pure TiO2. Beyond the optimum content of 2wt% Cu and Co, a decline in photocatalytic performance was observed which was ascribed to metal agglomeration and blockage of the photosensitive TiO2 surface.

Preparation of multiple-doped TiO2 nanotube arrays with nitrogen, carbon and nickel with enhanced visible light photoelectrochemical activity via single-step anodization

The main objective of this research is to enhance the photocatalytic activity of TiO2 nanotube aligned arrays (TNAs) for the visible light by multiple-doping with nitrogen, nickel and carbon for the first time. This has been achieved through anodization of titanium foils in ethylene glycol based electrolytes containing NH4F and various concentrations of K2[Ni(CN)4]. The method proposed allows for a simple one-step multiple-doping of TNAs during its electrochemical formation. The surface morphology, structure and composition of undoped and Ni–N–C-doped TNAs were investigated by field emission scanning electron microscopy (FESEM), XRD, XPS and EDX. The characterization results indicate that Ni, N and C atoms have been incorporated into the lattice of the TiO2 nanotubes. UV–Vis DRS spectroscopy and photo-electrochemical measurements showed that multiple-doping results in the broadening of the absorption region of visible light and the reduction of bandgap energy. Accordingly, multiple-doping of TNAs improves photogenerated electron–hole separation and increases transfer rate of surface charge carriers from the interior to the surface of semiconductors. Under the visible-light irradiation, the average photocurrent density of the optimal multiple-doped TNAs is 10 times greater than that of the undoped TNAs tested under the same conditions. Accordingly, Ni–C–N-doped TNAs may be considered as a promising photocatalytic material for various potential applications like water splitting under sunlight irradiation for hydrogen generation.

Fabricaion of improved novel p–n junction BiOI/Bi2Sn2O7 nanocomposite for visible light driven photocatalysis

A series of novel p−n junction photocatalysts BiOI/Bi2Sn2O7 (BiOI/BSO) were successfully fabricated via a facile hydrothermal method. The phase structures, morphologies and optical properties of the as-prepared samples were studied by XRD, TEM, HRTEM, BET, XPS, UV–vis DRS and photoluminescence (PL) spectroscopy. The results showed that BiOI/BSO heteronanostructures displayed much higher photocatalytic activity than pure BSO and BiOI for the degradation of rhodamine B (RhB). The best photocatalytic activity of BiOI/BSO with almost 99.9% RhB degradation situated at molar percentage ratio of 4% after 6h irradiation. The enhanced photocatalytic performance of BiOI/BSO could be mainly attributed to the formation of the heterojunction between p-BiOI and n-BSO, which effectively restrains the recombination of photoinduced electron–hole pairs. Moreover, the study of radical scavengers affirmed that h+ and •O2− were the primary reactive species for the degradation of RhB.

A novel synthesis of P/BiPO4 nanocomposites with enhanced visible-light photocatalysis

Using red phosphorus as precursors, P/BiPO4 composites were synthesised successfully via a facile hydrothermal method by the reaction between amorphous red (P) and Bi(NO3)3 aqueous solution without any additive. The phases structures, morphologies and optical properties of the obtained samples were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FTIR), Scanning electron microscopy (SEM), Energy-dispersive X-ray (EDX), UV–Vis DRS and photoluminescence spectroscopy (PL). The P/BiPO4 composite photocatalyst displayed much higher photocatalytic performance for a typical dye pollutant methylene blue (MB) degradation than the BiPO4 synthesised by a typical method under simulated visible light (λ>400 nm) and exhibited more enhanced catalytic efficiency than BiPO4 synthesised by a typical method. The excellent performance can be attributed to the high separation capacity of photogenerated electron–hole pairs and demonstrated to be a promising photocatalytic material.

Sol–gel synthesized mesoporous anatase titanium dioxide nanoparticles for dye sensitized solar cell (DSSC) applications

Hierarchically structured titanium dioxide nanoparticles were successfully synthesized by the sol–gel method. The synthesized nanoparticles were subjected to powder X-ray diffraction, UV–Vis DRS spectroscopy, Brunauer–Emmett–Teller method, Barrett–Joyner–Halenda analysis, field emission scanning electron microscopy, high-resolution transmission electron microscopy and energy-dispersive X-ray analysis. The powder X-ray diffraction pattern shows that the obtained particles are of anatase phase with good crystallite nature. The nitrogen adsorption and desorption isotherms show that the prepared material has surface area of 31.71 m2 g−1 and the pore size distribution analysis shows the average pore diameters of mesoporous TiO2 nanostructures to be 7.1 and 9.3 nm. The UV–Vis DRS spectrum shows that the TiO2 nanoparticles are having absorption in the ultraviolet region. The optical band gap of the nanoparticles is 3.2 eV. The morphological studies show the morphology of the particles as spherical in shape. The elemental compositions of TiO2 nanoparticles were confirmed by energy-dispersive X-ray spectrum analysis. The conversion efficiency of the solar cell was 3.415% with open-circuit voltage (V oc), short-circuit current (J sc) and fill factor (FF) of 0.607 V, 13.206 mA cm−2 and 42.56%, respectively.

Preparation, characterization and photocatalytic performance of pyrolytic-tire-char/TiO2 composites, toward phenol oxidation in aqueous solutions

A pyrolytic char/TiO2 (PC/TiO2) composite material, where PC was derived from recycled tires, was prepared by the sol–gel method. XRD analysis showed formation of TiO2 anatase phase, as well as, a small fraction of brookite phase. UV–vis DRS spectroscopy showed that PC/TiO2 composites have enhanced absorption at visible wavelengths 340–450nm. The photocatalytic activity and the promoting effect of PC/TiO2 composite catalysts were investigated for the degradation of phenol in aqueous suspensions. The photocatalytic degradation followed pseudo-first order kinetics. The ratio TiO2:PC (w:w) largely affected the performance of the composite catalysts. The optimal (w:w=0.1) ratio was found e.g., (0.2g PC, 2g TiO2). An important finding is a significant promoting effect of PC on the photocatalytic performance of TiO2. Electron paramagnetic resonance (EPR) spectroscopy showed that the pyrolytic char acts as a very efficient electron-acceptor from TiO2 particles under UV–vis irradiation. This resulted in decreased electron–hole pair recombination and subsequently in enhanced production of OH-radicals that oxidized phenol. Thus, PC matrix can act as an electron storage matrix for photo-induced electrons from TiO2.

Novel high potential visible-light-active photocatalyst of CNT/Mo, S-codoped TiO2 hetero-nanostructure

The current study deals with synthesize of novel nanophotocatalysts of CNT/Mo,S-codoped TiO2 by reacting between titanium isopropoxide (Ti(OC3H7)4) and CNT in aqueous ammonia and subsequent calcining of hydrolysis of the products. The prepared catalysts were characterized by N2 adsorption–desorption measurements, XRD, SEM, TEM, EDX, FT-IR, and UV–vis DRS spectroscopy. SEM and TEM images exhibited uniform coverage of CNT with anatase TiO2 nanoclusters. It was also demonstrated that the presence of S and Mo within the TiO2 acts as electrons traps and prevents the charge recombination and also enables the TiO2 photocatalyst to be active in visible-light region. Moreover, the CNT/Mo,S-doped TiO2 nanohybrids has been proven to has a excellent photocatalytic performance in photodecomposition of Congored (CR), at which the rate of decomposition reaches 100% in only 20 and 30min under UV and visible-light irradiation, respectively. The enhanced photocatalytic activity was ascribed to the synergetic effects of excellent electrical property of CNT and metal–non-metal codoping. Finally, which to best of our knowledge is done for the first time, we have demonstrated that Mo- and S-doped TiO2 decorated over CNT, or CNT/Mo,S-codoped TiO2, may have high potential applications in photocatalysis and environmental protection with superior catalytic activity under visible-light illumination.

Luminescent hybrid materials based on zeolite L crystals and lanthanide complexes: Host–guest assembly and ultraviolet–visible excitation

Several kinds of host–guest hybrid materials have been synthesized employing a ship in a bottle method by loading 9-hydroxy-2-methylphenalenone (MHPO) or 9-hydroxyphenalen (HPNP) from gas phase into the nanochannels of Ln3+-exchanged zeolite L (ZL) crystals (Ln=Gd or Eu). The resulting hybrids without lanthanide ions, MHPO–ZL, HPNP–ZL and the hybrids with lanthanide ions Ln–MHPO–ZL and Ln–HPNP–ZL are characterized with FT-IR, UV–vis DRS and photoluminescence spectroscopy. The photoluminescence properties of these hybrid materials have been analyzed and discussed, exhibiting the luminescence of Eu3+ and ligands under the excitation at ultraviolet–visible region. These results provide useful data and can be expected to have potential application in the practical fields.