Absorption In Visible Light Region Research Articles

Synthesis of a novel Z-scheme Ag/WO3/g-C3N4 nanophotocatalyst for degradation of oxytetracycline hydrochloride under visible light

In this work, Ag/WO3/g-C3N4 (AWC) nanocomposites were successfully prepared via a hydrothermal method. Oxytetracycline hydrochloride (OTC) was used to evaluate the photocatalytic activity of the photocatalysts under visible light. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectra (Raman), scanning electron microscope (SEM), Ultraviolet–visible spectroscopy (UV–vis DRS), photocurrent density (I-t) and electrochemical impedance spectra (EIS). The results showed that WO3 and Ag nanoparticles were coupled with g-C3N4 successfully. Comparing with pure WO3 or g-C3N4, the visible light absorption region of AWC composites was effectively broadened. The photocatalytic performance experiment illustrated that AWC-2 composite had the highest photocatalytic activity, and 97.74% of OTC (10 mg/L) was degraded in 60 min with 0.4 g/L of AWC-2. The radical scavenging experiments indicated that the superoxide radical (•O2−) and hydroxyl radical (•OH) were the most important active species for OTC oxidation. The five cycle photocatalysis experiment further proved that AWC is a stable photocatalyst for degradation of OTC. Finally, the possible degradation mechanism of Z-scheme heterostructure photocatalysis was proposed according to the experimental results.

Rational copolymerization strategy engineered C self-doped g-C3N4 for efficient and robust solar photocatalytic H2 evolution

Graphitic carbon nitride (g-C3N4) with unique physicochemical features has garnered much attention in artificial photosynthesis, yet the photoactivity of pristine g-C3N4 (PCN) is severely restricted because of its rapid charge recombination rate and narrow visible-light absorption. To this end, for the first time, here we reported a rational one-step copolymerization strategy for the fabrication of carbon self-doped g-C3N4 (CCN) by using melamine and chitosan as the starting materials. Experimental results indicated that the bridged N atoms were substituted by C atoms in the g-C3N4 matrix, resulting in the formation of delocalized big π bonds, thereby the obviously increased the electrical conductivity, remarkably extended the visible-light absorption region, and significantly improved the mobility of photoinduced electron-hole pairs. Consequently, the as-engineered CCN with abundant mesopores structure showed a dramatically boosting photocatalytic H2-evolved activity (1224 μmol g−1 h−1), 4.5-folds than PCN powders. Eventually, the resulting CCN exhibited an extremely long-term durable stability after storing in reaction solution for 90 days. Our work will bring about potential application in designing of high-performance g-C3N4 photocatalyst for renewable solar-to-H2 conversion.

Preparation of WS2–TiO2–Au using hydrothermal synthesis for photocatalysis under visible light

In this study, the preparation of ternary photocatalyst using a simple hydrothermal method is shown with high performance. A ternary composite consisting of tungsten sulfide (WS[Formula: see text] nanosheets, titanium oxide (TiO[Formula: see text] and gold (Au) nanoparticles is used to the extend the visible-light absorption region of TiO2. The morphological and spectroscopic natures of the prepared sample were analyzed using scanning electron microscopy (SEM), Raman spectroscopy and ultraviolet–visible (UV–vis) photospectroscopy. The photocatalysis measurement for photodegradation of methylene blue dye was performed under the visible light. The photocatalytic studies suggest that in the ternary composite, consisting of three materials with different energy levels, the electrons excited form a cycle to lower the probability for the recombination of electron–hole pairs enhancing the property of photocatalytic activity of TiO2.

Facile synthesis of clinoptilolite-supported Ag/TiO2 nanocomposites for visible-light degradation of xanthates

A novel ternary Ag/TiO2/clinoptilolite (ATC) nanocomposite was synthesized via a two-step synthesis strategy by combining the hydrothermal and in-situ reduction process. The obtained samples were characterized by a series of methods of XRD, SEM, TEM, N2 adsorption-desorption isotherms, XPS, FTIR, and UV-vis DRS. It is revealed that Ag and TiO2 nanoparticles were tightly bonded with the clinoptilolite and well-dispersed on its surface. Xanthates were employed as the target pollutants to evaluate the photodegradation efficiency of the as-synthesized samples. Particularly, the ATC photocatalyst exhibited an improved visible-light-induced photodegradation performance towards xanthates, which was much superior to those of binary Ag/TiO2 and Ag/clinoptilolite nanocomposites. The key influencing factors were also investigated to obtain optimal degradation conditions. The excellent photocatalytic performance of the ATC nanocomposites mainly benefited from the enlarged adsorption capacity, visible-light absorption region, and charge separation efficiency. The possible photodegradation mechanism was proposed according to the results of real-time spectral evolution, trapping experiment, and UV-vis DRS.

A Two-dimensional Amorphous Plasmonic Heterostructure of Pd/MoO3-x for Enhanced Photoelectrochemical Water Splitting Performance.

Two-dimensional (2D) heterostructures based on localized surface plasmon resonance (LSPR) have a great potential for solar energy harvesting applications. Exploring 2D amorphous plasmonic heterostructures with high light absorption and catalytic activity is desirable yet challenging. Herein, 2D Pd/MoO3-x amorphous heterostructures can be obtained by immobilizing Pd single atoms in unsaturated coordination sites of amorphous MoO3-x , because of strong metal-support interactions, and it reaches a current density of 50 μA cm-2 for photoelectrochemical response with good durability, and exhibits a high incident-photon-to-current-conversion efficiency (IPCE) of 14.8% at 460 nm. Such an enhanced catalytic effects are contributed to the enhanced light absorption in visible region and change of electronic structure owing to enhanced electron transfer through dominant Pd-O bonds, which facilitate water splitting. This work moves a step closer to the expansion of photovoltaic device with the high conversion efficiency for visible light for amorphous heterostructures.

Improved third-order optical nonlinearities in Ag/MoS2 Schottky-type nano/hetero-junctions

Molybdenum disulfide (MoS2) nanostructures have been prepared by a hydrothermal treatment and were decorated with metallic silver (Ag) using the conventional wet incipient impregnation process to form Ag/MoS2 nano/hetero-junctions. The physiochemical functionalities were characterized using X-ray diffraction, Fourier transfer infrared spectroscopy, Raman spectroscopy, field emission scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscopy. UV–Vis (ultraviolet–visible) spectroscopy shows an improved light absorption in visible region for Ag/MoS2 nano/hetero-junctions due to the surface plasmon resonance absorption. Photoluminescence (PL) studies suggest efficient photoexcited charge separation to occur in Ag/MoS2 nano/hetero-junctions due to an internal electric field formed across Schottky interface. The nonlinear responses of as-prepared samples to intense laser fields were examined using standard single-beam Z-scan technique under a 532 nm CW second-harmonic Nd:YAG laser irradiation wherein demonstrated reverse saturable absorption behaviors and self-defocusing responses due to negative lens effects were observed. The third-order nonlinear refractive index and absorption coefficient for Ag/MoS2 nano/hetero-junctions were found to be 6.5 × 10-7 cm2/W and 3.5 × 10-4 cm/W, respectively, showing 1.44 and 1.5 times enhancement than in MoS2 nanostructures.

Study of structural, electronic and optical properties of co-doped CeO2 using the density functional theory (DFT) method

The (B, C), (B, H), (B, N), (B, O), (B, P) and (B, S) co-doping effects on structural, electronic and optical properties of CeO2 systems have been studied to determine their potential for photo-catalytic activity using density functional theory and Hubbard U method. Both metallic and nonmetallic co-doping of elements show increase in cell volume and produce local lattice distortion. Due to this co-doping, energy gap between valence and conduction bands becomes narrower than that of pure CeO2, which provides easy way for the transfer of electrons from oxygen 2p orbitals to Ce 4f orbitals assisting in the process for photo-catalysis. Atomic orbitals of similar energy are mixed together except for the atomic s orbital of hydrogen atom. Further, optical absorption peaks for (B, C), (B, H) and ((B, N) co-doped CeO2 systems are found at higher energy range (blue shift) predicting to be better photo-catalytic material. Co-doped CeO2 materials are expected to speed up photoreaction and more electromagnetic waves are allowed to pass through them. Co-doping causes impurity levels to appear in the forbidden energy gap. Extended visible light absorption region has been observed leading to photo-catalytic activity enhancement for the visible light range (~1.5–6.2 eV).

Improved charge carrier dynamics through a type II staggered Ce MOF/mc BiVO4 n-n heterojunction for enhanced visible light utilisation

3D heterostructure of varied compositions between monoclinic BiVO4 and Cerium (Ce) Metal Organic Framework (MOF), possessing donor-acceptor characteristic was synthesized through facile hydrothermal technique. Molecular modelling was performed to understand the electronic structure and chemical bonding environment of BiVO4. The composite showed a reduction in bandgap to 2.20 eV and enhanced the light absorption in visible region with enhanced light absorbance. Band edge position calculation revealed the formation of type II staggered heterojunction. Such junction resulted a built-in electric field that prevented the exciton recombination with a lifetime of 5.8 µs. Ce MOF acted as an electron sink that received the excited electrons from BiVO4 and reduced the luminescence and charge transfer resistance to 17.3 Ω. The reduction in Debye length and increase in the carrier density favored the electronic movement around the junction interface. The superiority of this 3:1 composition was evaluated against removing methylene blue, Rhodamine B, and methyl orange with 88.8%, 86.07% and 74.7% degradation ratio, respectively. Similar excellent catalytic performance was also achieved for the phenol of non-photosensitizing nature with 51.3% removal efficiency. Active species trapping showed the h+ played a dominant role amongst the Reactive Oxygen Species (ROS) for the removal of studied pollutant from water.

The Enhancement of Visible Absorption of Cu Doped ZnO Nanorods on Patterned Substrates

: We report the antireflection and light absorption in visible region by new stretchable substrates with patterned structure. Mogul substrates with 3-Dimentional structures were fabricated by using polydimethyl – siloxane that imitate the nanostructures surface. Then, Copper doped ZnO NRs on mogul-patterned surface by hydrothermal method at low temperature. The optical properties, morphology and structures of ZnO:Cu NRs were investigated through out of measurement the scanning electron microscopy, X-Ray diffraction and ultraviolet-visible spectroscopy, respectively. The results show the Cu doped ZnO NRs were uniformly and dense grown on mogul substrates, well oriented in the (002) plane. Additionally, the light absorption can be significantly enhanced to more 10% in a wide spectral range (400-800 nm) due to the reduce reflection. Growing ZnO NRs doping on new stretchable substrates with a mogul-patterned surface were successfully fabricated and applicable in the flexible and stretchable optoelectronic devices.

Fabrication of coatings based on strontium-bismuth-silicate photocatalyst for water purification from organic pollutants

Strontium-bismuth containing photocatalytic active coatings on a silicate carrier using sorbite-nitrate pyrolytic synthesis were obtained. The effect of strontium-bismuth molar ratio in the precursor mixture on the phase composition, boundaries of the visible light absorption region and photocatalytic activity of the coatings obtained were studied. The best photocatalytic activity is achieved by coatings obtained from the precursor mixture at Sr:Bi molar ratio of (1:3) and (1:4) in the experiment with a model organic pollutant — methylene blue (MB). The obtained photocatalytically active coatings on silicate carrier (Sr:Bi-1:4) were tested in a water purification unit (WPU) at different rotation speeds. The effective range of rotation of samples without loss of photocatalytic properties at photo-oxidation of MB (15–35 rpm) was established.

Effect of heavy ions irradiation on LiTaO3 crystal

In this work, congruent LiTaO3 crystals are irradiated by heavy ions Fe, Xe, and Bi respectively at fluence range of 1 × 1012 ~ 2 × 1015 cm−2. The effects of heavy ions irradiation are studied by using optical transmission spectroscopy, Rutherford backscattering, optical microscopy, X-ray diffraction.Heavy ion irradiation presents a unique effect in transmission spectra which is quite opposite to the previous reported results of light ions irradiation. The latter could often cause a significant optical absorption in visible light region. The former, however, not only induce no optical absorption, but can enhance transmittance over a broad spectral range (340–2500 nm). It is found that the discrepancy may originate from different damage process during ions irradiation. Light ion irradiation can create numerous of simple defects (like oxygen vacancies) serving as color centers which can cause an optical absorption. However, direct amorphization dominates the damage process induced by heavy ions, during which it hardly produces simple defects. Moreover, due to direct heavy ions bombardment, special textures are formed on the surfaces of the samples which serve as antireflection structures and enhance optical transmissions.

Role of annealing temperature on the properties of SrO nanoparticles by precipitation method

Strontia nanoparticles are successfully prepared by chemical precipitation method. The SrO nanoparticles are characterized by XRD, UV-DRS and I-V analysis. X-ray diffraction peaks reveal the single-phase polycrystalline tetragonal structure with preferential orientation along (2 0 2) direction. Influence of annealing temperature strongly induce the growth of peak which indicates the increased intensity of (202) peak. The heat treatment strongly distresses the growth of triplet peaks (002), (101) and (110) whereas the same augment the growth of (202) and (310). Strontium oxide nanoparticles would allow more light for absorption in UV region due to its rough surface whereas the same would allow moderate light absorption in visible region due to its high packing density. The expansion and contraction of Sr-O bonds leads to a high crystalline nature with its purity at 322 nm. It is proposed that strain and surface defects in SrO nanocrystal take place due to different absorption edge.

A novel photocatalytic platform based on the newly-constructed ternary composites with a double p-n heterojunction for contaminants degradation and bacteria inactivation

Visible-light-induced photocatalytic technique is regarded as the most promising approach to tackle environmental pollution. Herein, a novel ternary MIL-88B@COF-200@10%PANI composite with a double p-n heterojunction was firstly synthesized through a step-by-step self-assembly strategy. Current results suggested that bimetallic Fe.Co-MIL-88B displayed excellent photocatalytic activity, and its combination with spherical COF-TPA/TPB effectively promoted separation and transfer of photoinduced carriers. Meanwhile, introducing PANI with π-π conjugated structure acted as a “bridge” of the charge transport could further boost carrier mobility and enhance absorption in visible light region. Benefiting from the formation of double p-n heterojunction, the recombination of photogenerated electron-hole pairs was inhibited effectively, thereby improving the photocatalytic activity. More significantly, in comparison with pristine COF-TPA/TPB, Fe.Co-MIL-88B and PANI, the MIL-88B@COF-200@10%PANI composite not only presented excellent degradation ability for various contaminants, but also exhibited superb sterilization effect for E. coli and S. aureus. The OH, O2−, h+ and e− were main active species in the photocatalytic reaction system, which were responsible for pollutant degradation and bacteria inactivation. Furthermore, it was proved by our experiment results that the separation and transfer routes of photogenerated charge carriers followed a traditional type-II heterojunction mechanism. All in all, this study could provide novel insights for preparation and application of highly efficient photocatalyst in future research.

First-principles study on the type-II g-C6N6/GaS heterojunction: A promising photocatalyst for water splitting

The electronic transport properties, photocatalytic reaction mechanism and optical properties of novel g-C6N6/GaS heterojunction are investigated by first-principles calculations in this work. The results demonstrate that g-C6N6/GaS forms a type-II heterojunction with the band edge straddling the redox levels of water and satisfying the requirements for overall water splitting reactions. Driven by the band offset and the built-in electric field at the interface, the photogenerated electrons and holes flow to the conduction band of g-C6N6 and the valence band of GaS, respectively. The effective separation of electron-hole pairs in space benefits to improve the photocatalytic efficiency. In addition, g-C6N6/GaS heterojunction exhibits excellent optical absorption in visible light region. Therefore, the g-C6N6/GaS heterojunction is a promising candidate for photocatalytic overall water splitting and solar energy conversion.

P- and F-co-doped Carbon Nitride Nanocatalysts for Photocatalytic CO2 Reduction and Thermocatalytic Furanics Synthesis from Sugars.

A new P- and F-co-doped amorphous carbon nitride (PFCN) has been synthesized via sol-gel-mediated thermal condensation of dicyandiamide. Such synthesized P- and F-co-doped carbon nitride displayed a well-defined mesoporous nanostructure and enhanced visible light absorption region up to infrared with higher BET surface area of 260.93 m2 g-1 ; the highest recorded value for phosphorus-doped carbon nitride materials. Moreover, the formation mechanism is delineated and the role of templates was found to be essential not only in increasing the surface area but also in facilitating the co-doping of P and F atoms. Co-doping helped to narrow the optical band gap to 1.8 eV, thus enabling an excellent photocatalytic activity for the aqueous reduction of carbon dioxide into methanol under visible-light irradiation, which is fifteen times higher (119.56 μmol g-1 h-1 ) than the bare carbon nitride. P doping introduced Brønsted acidity into the material, turning it into an acid-base bifunctional catalyst. Consequently, the material was also investigated for the thermal conversion of common carbohydrates into furanics.

Late-model g-CNQDs/H3PW12O40/TiO2 heterojunction nanocatalyst with enhanced photocatalytic performance

The g-CNQDs/H3PW12O40/TiO2 heterojunction photocatalytic material is fabricated by facile ultrasonic method. The crystal structure, elemental composition, morphology and optical properties of as-synthesized catalysts are investigated by a series of characterizations. Studies have shown that g-CNQDs have been successfully doped into H3PW12O40/TiO2. The introduced g-CNQDs are uniform in size and have an average diameter of 5.8 nm. The 5% g-CNQDs/H3PW12O40/TiO2 shows the highest degradation efficiency of 99.3% toward RhB under simulated sunlight for 30 min, which is 5.68 times than of H3PW12O40/TiO2 under same conditions. The improved photocatalytic activity of the g-CNQDs/H3PW12O40/TiO2 ternary system is attributed to the expansion of visible-light absorption region and diminishing photoelectron–hole recombination. The testing of radical scavengers demonstrated that the main active species in the photocatalytic process involving three active species are ·O2− and ·OH, and the holes (hVB+ ) play an auxiliary role. The photodegradation efficiency of g-CNQDs/H3PW12O40/TiO2 ternary composite catalyst is reduced by 6.2% after five cycling runs. The present work proposes an efficient optimization of the fabrication of potent and stable TiO2-based photocatalysts driven by sunlight.

Noble-metal free photocatalytic hydrogen generation of CuPc/TiO2 nanoparticles under visible-light irradiation

Development of visible-light activated photocatalysts is highly important but challenging for photocatalytic reactions. In addition, noble-metal cocatalysts are crucially required for efficient charge transfer in most solar water splitting reactions. In the present study, we have synthesized copper phthalocyanine (CuPc) supported TiO2 photocatalyst composites by a facile solution reaction and demonstrated their efficient photocatalytic hydrogen generation under visible-light irradiation. The amorphous CuPc coating layer plays key roles in solar water splitting in terms of efficient separation of the photogenerated charges and high absorption in visible-light region. More surprisingly, our CuPc/TiO2 does not demand any noble-metal cocatalyst for exhibiting high photocatalytic activity with 6.68% of apparent quantum yield (AQY) at 420 nm. Moreover, several continuous runs of hydrogen generation using CuPc/TiO2 composite proved the high durability of our products. The detailed charge transfer dynamics of CuPc/TiO2 composites by time-resolved photoluminescence (TRPL) demonstrated that our noble metal-free CuPc/TiO2 shows a comparably high charge transfer efficiency as that of Pt cocatalyst modified samples. On the basis of the analysis, a possible mechanism for visible-light driven photocatalytic hydrogen generation of CuPc/TiO2 composites is postulated. Our study suggests that CuPc/TiO2 is a highly efficient and stable photocatalyst for solar water splitting even without noble-metal cocatalysts.

2D XBiSe3(X = As, Sb) monolayers with high anisotropic mobility and enhanced optical absorption in visible light region

Configurations and properties of 2D XBiSe3(X = As, Sb) monolayers are predicted by first-principles calculations. Dynamic and thermal stabilities are affirmed by phonon dispersion and ab initio molecular dynamics simulation, respectively. Bandgap and band edges, density of states, optical absorptions, and mobilities are calculated by using the obtained structures. Effects of strain engineering on the band structure and optical absorption are also explored. Results reveal that the AsBiSe3 and SbBiSe3 monolayers have indirect gaps of 1.2 eV (HSE06)/1.43 eV (GW) and 1.1 eV (HSE06)/1.32 eV (GW), respectively. The high electron (approximately 105 cm2V−1s−1) and hole (approximately 104 cm2V−1s−1) mobilities of the XBiSe3 monolayers are observed for zigzag and armchair directions, and obvious anisotropy is observed. The intense optical absorptions in the UV–visible light regions are identified for the two monolayers. Interestingly, the band edge of the AsBiSe3 monolayer can span the redox potential of water under −4% biaxial compressive strain, which implies that this monolayer can be used as a candidate material for photocatalytic water splitting to produce hydrogen. All the results support the assertion that the XBiSe3 monolayers have potential for application in the optoelectronic, photocatalytic, and photovoltaic fields.

Fabrication and characterization of a novel Fe(Ⅲ) modified C-doped Cr2O3 photocatalyst for cyclohexane oxidation to cyclohexanone with ultrahigh selectivity

The grafting of Fe(Ⅲ) cocatalysts onto the surface of C-doped Cr2O3 derived from MIL-101(Cr) has been successfully achieved via a simple precipitation. The obtained Fe(Ⅲ) modified C-doped Cr2O3 photocatalyst has been investigated by cyclohexane oxidation to cyclohexanone and some physicochemical characterizations like XRD, BET, ICP-MS, SEM TEM XPS FT-IR, SPV, PL, ESR and UV–vis-DRS. The results reveal that the Fe species are exited in a +3 state and uniformly disperse on the surface of the C-doped Cr2O3. The Fe@C/Cr2O3 samples possess a broad visible light absorption region and exhibit super photocatalytic activity and selectivity for cyclohexane oxidation to cyclohexanone. Fe(Ⅲ)could be considered as a reduction site for largely improving the formation of superoxide radical anion from oxygen molecule in the photocatalytic reaction, which induces a high photocatalytic activity for cyclohexane oxidation. Compared with C/Cr2O3, the photocatalytic activity of Fe@C/Cr2O3 could be increased by up to six times at room temperature. Moreover, the ultrahigh selectivity (99.77%) for cyclohexanone is obtained. The high photocatalytic activity and cyclohexanone selectivity is attributed to the improved generation of cyclohexyl radicals and superoxide radical anions due to the Fe(Ⅲ)modified surface of C-doped Cr2O3photocatalyst under the controlled photocatalytic reaction condition.

Theoretical study of (TM)FeO3 (TM = 3d transition metals) molecular clusters

Time-dependent density functional theory–based calculations were carried out to comprehensively investigate the structural, electronic, and optoelectronic properties of series of molecular clusters (TM)FeO3 (with TM = 3d elements). The structures were studied at different levels of theory to explore the electronic energy levels, charge transfer analysis, and UV-Vis excitation spectra. In order to predict viable charge states and ordering of TM moments, the calculations were performed at different spin values to consider low-spin and high-spin configurations. The magnetic moments of the series of clusters in most stable configuration increased for the clusters with Sc to Fe and then decreased to Zn. The calculated values of magnetic moment and binding energy of the clusters show nearly a reciprocal trend. The substitution of TM, in order of increasing atom number from Sc to Zn, appeared to modify the optical response and shifted the absorption features of the clusters from ultraviolet to the visible region. The clusters CoFeO3, NiFeO3, CuFeO3, and ZnFeO3 are found suitable for coating on TiO2 and ZnO to increase light absorption in visible region. Owing to the findings of this study, the series of the clusters are predicted to be used in photocatalytic water splitting, photoanode material in dye-sensitized solar cell, supercapacitors, and electrode materials.