Recombination Rate Of Charge Carriers Research Articles

Properly aligned band structures in B-TiO2/MIL53(Fe)/g-C3N4 ternary nanocomposite can drastically improve its photocatalytic activity for H2 evolution: Investigations based on the experimental results

The development of new tools that could meet the demand of sustainable energy production has attracted worldwide scientific attention. Over the past few decades, significant research efforts have been carried out to efficiently reduce water to H2 (green fuel) over semiconductor photocatalysts. Numerous semiconductor photocatalysts have been employed in photocatalysis for optimum H2 production. All the techniques were chosen based on their flexibility, cost-effectiveness, and ease of availability. Recently, polymeric carbon nitride (g-C3N4) received worldwide attention in visible light photocatalysis for energy and environmental applications due to its low price, robust nature, and superior thermal stability. Nevertheless, g-C3N4 (CN) exhibits shortfalls such as high charge carrier's recombination rate and weak reduction ability. To overcome these drawbacks, herein, for the first time we have fabricated B-TiO2/MIL-53(Fe)/CN ternary composite via hydrothermal and wet-chemical methods. The resultant B-TiO2/MIL53(Fe)/CN ternary composite shows drastically improved photocatalytic activity for hydrogen evolution compared to the bare CN, B-TiO2, and MIL53(Fe) components. The B-TiO2/MIL53(Fe)/CN ternary composite produced approximately 166.3 and 581.2 μmol h−1 g−1 of hydrogen under visible light and UV–visible light irradiations, respectively, with the assistance of co-catalyst Pt. Photo-luminescence (PL) and the fluorescence (FL) spectroscopy measurements reveal that the enhanced photoactivity is due to the greatly promoted charge carrier's separation and transfer at the interfacial contact of the well-aligned three-component systems. This work will promote the design and development of efficient photocatalyst based on CN for clean energy production and environmental purification.

Mesoporous-assembled TiO2-NiO-Ag nanocomposites with p-n/Schottky heterojunctions for enhanced photocatalytic performance

Construction of Schottky heterojunctions with plasmonic metals and p-n heterojunctions with p-type semiconductors have been considered as two effective approaches for boosting photocatalytic activity of TiO2. Here, we report on a magnetically-recyclable TiO2-NiO-Ag p-n/Schottky heterojunction photocatalyst fabricated by a facile and two-step approach combining spark discharge generation of mixed metallic nanoparticles under a protective argon atmosphere and a suitable thermal annealing process at air. Our comprehensive characterization studies revealed the formation of a mesoporous nano-heterostructure consisting of defective TiO2 nanoparticles that were finely incorporated with well-dispersed p-type NiO and Ag nanoparticles. Thanks to its extremely high surface area (223.07 m2 g−1), reduced optical band gap (~1.88 eV), improved visible-light absorption (~26% within 400–900 nm), and suppressed charge carriers recombination rate, our structure exhibited an enhanced photocatalytic degradation efficiency of 93.8% and a mineralization efficiency of 87.5% within 90 min irradiation towards methylene blue decomposition, superior to those of pure TiO2, NiO, and TiO2-NiO samples. This nanocomposite structure shows a large potential for practical application in the areas of environmental remediation and other photocatalytic applications.

Preparation and application of defective graphite phase carbon nitride photocatalysts

With the development of industry and agriculture, the problems of environmental pollution and energy shortage have become increasingly severe. Semiconductor photocatalysis technology is one of the effective ways to solve environmental pollution and energy crisis. The principle of photocatalysis is based on the oxidation-reduction ability of photocatalysts under light conditions, which can achieve the purposes of purification of pollutants, material synthesis and transformation. Graphite phase carbon nitride (g-C3N4), as a new high-efficiency catalyst, has good stability and shows great engineering application potential in photocatalytic technology. However, the unmodified g-C3N4 has a limited visible light response range, and the photo-excited charge carrier recombination rate is high, resulting in low photocatalytic activity. Nitrogen defects are introduced into the g-C3N4 framework. These defects can manipulate the electronic structure, and the interstitial state produced can be used as a band-tail state, which can overlap with the valence band or the conduction band. The mid-gap state of semiconductors can extend the light response and act as an active center for electron-hole excitation. Introducing defects into g-C3N4 can improve the photocatalytic activity of g-C3N4. This paper systematically reviews the physical, chemical and electrochemical properties of g-C3N4 on the basis of experimental and theoretical research progress. The synthesis methods of defect g-C3N4 are summarized, including adjustment before polymerization, adjustment during polymerization, and adjustment after polymerization. The adjustment before polymerization is to introduce defects by changing the precursor, such as adding hydroxide, sodium borohydride and other substances to the precursor. The adjustment during polymerization is to provide a reducing atmosphere during polymerization can prepare g-C3N4 with different nitrogen-vacancy densities, such as hydrogen, ammonia and so on. The adjustment after polymerization is to modify the synthesized defect-free g-C3N4, such as recalcining or acid treatment to achieve the purpose of synthesizing nitrogen vacancies. The effect of defect sites on g-C3N4 is also discussed. The intermediate state induced by nitrogen defects can be transformed into active centers excited by electron holes, and the optical response of defect g-C3N4 is broadened due to the narrowing of the band gap. In the range, nitrogen defects can trap photo-generated carriers and prevent their recombination, thereby increasing the overall quantum efficiency. However, excessive introduction of nitrogen defects will produce deeper interstitial states. These deeper interstitial states can not only capture photo-generated electrons, but also photo-generated h+, which then become the recombination sites of photo-generated carriers. In addition, we separately summarized the application of the defect g-C3N4 in water treatment, such as the degradation of antibiotics and organic pesticides and the reduction of the toxicity of heavy metals, as well as water decomposition, carbon dioxide conversion and photocatalytic denitrification. Defect g-C3N4 has achieved good results in these applications. Although considerable progress has been made in the research of g-C3N4 in recent years, there are still many challenges in preparing g-C3N4 with high-efficiency catalytic performance. Finally, in view of the challenges faced by the application of defective g-C3N4, key discussions and future prospects are proposed from the aspects of mechanism exploration and material development.

Fabricating intramolecular donor-acceptor system via covalent bonding of carbazole to carbon nitride for excellent photocatalytic performance towards CO2 conversion

Photocatalytic conversion of CO2 into hydrocarbon fuels is an ideal technology of mitigating greenhouse effect caused by excessive emission of CO2. However, the high recombination rate of electron-hole pairs and limited charge carriers transport speed constrained the catalytic performance of many semiconductor catalysts. In this contribution, a series of carbon nitride (g-CN) samples with intramolecular donor-acceptor (D-A) system were successfully prepared by introducing organic donor into their structures. Characterization results confirmed that carbazole was successful connected to the structure of g-CN via chemical bond. The formation of intramolecular D-A system greatly enlarged the light response region of g-CN-xDbc. In addition, a new charge transfer transition mode was formed in g-CN-0.01Dbc due to the incorporation carbazole, which enable it to use light with energy lower than the intrinsic absorption of g-CN. Meanwhile, the D-A structure led to the spatial separation of electrons and holes in g-CN-xDbc and significantly decreased the recombination rate of electron-hole pairs. The g-CN-0.01Dbc presented the best catalytic performance and the CO evolution rate was 9.6 times higher than that of g-CN. Moreover, the reaction was performed in water without any additive, which made it green and sustainable. DFT simulation confirmed the D-A structure and charge carrier migration direction in the prepared samples.

Bismuth vanadate/MXene (BiVO4/Ti3C2) heterojunction composite: enhanced interfacial control charge transfer for highly efficient visible light photocatalytic activity.

We have synthesized BiVO4/Ti3C2 nanocomposite via a low-cost hydrothermal method and investigate its photocatalytic degradation activity against monoazo (methyl orange) and diazo dye (Congo red) in an aqueous solution under visible light. The physiochemical characterization exhibited that the addition of MXene in pristine BiVO4 nanocomposite led to an increase in specific surface area and reduction in optical band gap energy. MXene also helps in enhancing visible light response via a higher electron-hole pair generation rate and long lifetime. The synthesized BiVO4/Ti3C2 heterojunction composite exhibited 99.5 % degradation efficiency within 60 min for Congo red and 99.1 % for methyl orange solution in 130 min owed to a large specific surface area (1.79 m2/g), reduced band gap (1.99 eV), and low recombination rate of charge carriers. The chemical mechanism for BiVO4/Ti3C2 nanocomposite proposes that Ti3C2 role-plays as electron capture because of the higher potential of MXenes, tuning band gap energy which paves the way to excellent photocatalytic action. This work opens a new basis for developing Ti3C2 based promising and inexpensive co-catalyst for efficient solar utilization in photocatalytic-related applications in the future.

Facile one-step deposition of ZnO-graphene nanosheets hybrid photoanodes for enhanced photoelectrochemical water splitting

ZnO-graphene nanosheets photoanodes were deposited at room temperature by a one-step kinetic spray process on a titanium sheet from micro-sized ZnO and graphite powders. ZnO-graphene nanosheet hybrid photoanodes with varying graphite contents were utilized for studying photoelectrochemical (PEC) water splitting. The Raman spectra revealed the direct transformation of micro-sized graphite powder to graphene nanosheets in all hybrid photoanodes after the deposition process, without any post-treatment. Surface morphology analysis revealed the fragmentation of the micro-sized flake morphology to morphology composed of mixed nanorods and nanosheets. The optical properties of the ZnO-graphene nanocomposites were investigated by the diffuse reflectance and photoluminescence (PL) emission spectroscopy, which revealed the decrease of the optical band gap and quenching of PL intensity. The hybrid photoanode with 50 wt% graphite content revealed the smallest bandgap of 2.6 eV and the lowest emission intensity compared with other hybrid photoanodes, which demonstrated the inhibition of photogenerated charge carrier recombination rate as well as an improvement in the visible-light-harvesting. The PEC results exhibited an improvement of the photocurrent with the incorporation of graphene nanosheets due to the improved photogenerated charge transfer kinetics and separation. The hybrid photoanode with 50 wt% graphite content revealed the highest photo-response current of 4.82 mAˑcm−2 corresponds to photoconversion efficiency of 3.25% @1.23 V vs. RHE.

Degradation mechanism, reaction pathways and kinetics for the mineralization of Bisphenol A using hybrid ZnO/graphene oxide nano-catalysts

Removal of Bisphenol A (BPA) from surface waters is necessary before consumption. A study, therefore, was conducted to degrade BPA using graphene oxide, ZnO and ZnO decorated on graphene oxide. Hydrothermal method was used to synthesize the hybrid nano-catalysts. 99.5% photocatalytic degradation of BPA was achieved by using ZG0.6 nano-catalyst in comparison to bare ZnO and GO nano-catalysts at natural pH of 7.5 in 60 min of UV irradiation. The higher photocatalytic activity of ZG0.6 nano-catalyst could be ascribed to an improved surface area, efficient charge separation as well as the decreased recombination rate of electron-hole charge carriers, leading to the generation of highly reactive hydroxyl radicals for the degradation of BPA. Photocatalytic degradation followed Langmuir-Hinshelwood model with pseudo-first-order kinetics. The degradation mechanism is also detailed with identification of reaction intermediates. Degradation pathways, based on LCMS analysis, have been proposed. The pathways revealed the formation of smaller by-products such as phenol, hydroquinol and (Z)-3-hydroxyacrylaldehyde. The developed ZG0.6 nano-catalyst were found to be reusable for consecutive five runs without much loss in the activity and have the advantage of effective charge separation.

Newly designed ternary hematite-based heterojunction for PEC water splitting

Hematite is recognized as a promising photoanode for photoelectrochemical water oxidation to produce solar hydrogen due to its favorable properties. However, the high charge carrier recombination rate due to low electrical conductivity and sluggish oxygen reduction kinetics of pure hematite hinder its photocatalytic activity. This work proposed a new hematite-based heterostructure of Ti-Fe2O3/Fe2TiO5/FeOOH, synthesized through a hydrothermal method. The photoanode morphology was branched nanorods that expanded their surface area and improved charge transfer at the photoanode/electrolyte interface. In a novel and complement modification approach, a thin pseudobrookite interlayer was applied between β-FeOOH electrocatalyst and Ti-doped hematite to suppress charge recombination, and enhance charge separation, leading to 32% and 26% increase in photocurrent density and solar to current efficiency, respectively. The photoanode exhibited a great improvement with the photocurrent density of 1.63 mA/cm2 at V = 1.5 V vs. RHE and the total electrical resistance of 2.3 kΩ.cm2 compared to the pure hematite.

Heterostructured Ternary In2O3−Ag−TiO2 Nanotube Arrays for Simulated Sunlight‐Driven Photoelectrocatalytic Hydrogen Generation

AbstractThe ternary In2O3−Ag−TiO2 composites based on anatase TiO2 nanotube arrays (TNTs) were synthesized to extend the light responsive region, enhance the visible light absorption, reduce the recombination rate of charge carriers and promote the efficiency of water splitting for H2 evolution. Highly ordered TNTs were first prepared by electrochemical anodization of Ti sheets. Ag nanoparticles with a diameter of about 20 nm were then uniformly deposited inside and on the orifice of the TNTs. In2O3 nanoparticles synthesized through a solvent‐thermal method were subsequently modified on the Ag−TNTs using an ultrasound‐assisted electrophoresis method. In2O3−Ag−TNTs composites exhibited enhanced visible light absorption and photocurrent when compared to binary Ag−TNTs and In2O3−TNTs. As a result, the optimal hydrogen generation rate using the In2O3−Ag−TNTs composite under visible light irradiation was 1.92 μmol cm−2 h−1, 5 times higher than that of the pure TNTs.

Improvement of the depolluting and self-cleaning abilities of air lime mortars with dispersing admixtures

The aim of this study is to develop new air lime mortars with enhanced photocatalytic depolluting and self-cleaning abilities. Nanosilica, as pozzolanic mineral admixture, was used to improve the strength of mortars, whereas nanotitania (TiO2) was added to impart photocatalytic properties. At the same time, five different dispersing admixtures –superplasticizers– were added in bulk to the mortars to enhance the photocatalytic activity by reducing the rate of charge carrier recombination. Four polycarboxylate-based derivatives and a polynaphthalene sulfonate were tested aiming to achieve an efficient charge separation. In order to increase the lasting of the mortars subjected to water movements, sodium oleate was also added as a water repellent agent. Since the photoinduced hydrophilicity, responsible for the self-cleaning effect, might be affected by the water repellent, the compatibility between this admixture and the photocatalytic performance of the nanotitania was also investigated. Results showed that photocatalytic activity was improved due to the action of the superplasticizers as indicated by an average 33% increase of NO degradation, which is significant to the depolluting activity of these mortars. Furthermore, these mortars also showed a greatly reduced release of intermediate toxic compounds, mainly NO2: the selectivity factor (NOx/NO) reached values up to 87%. The self-cleaning ability, studied through dye degradation, of the mortars with SPs was also enhanced around 1.2 times. Three of the polycarboxylate-based superplasticizers enhanced the photosensitization of the dye under visible light irradiation, resulting in faster decolouring kinetics. In connection with the self-cleaning performance, these same SPs preserved the photoinduced hydrophilicity of the lime mortars, reaching good wettability of the surface of the mortars (water contact angles of ca. 10°), even in the presence of the sodium oleate, proving the compatible characteristics of the admixtures and allowing obtaining a new range of actively depolluting lime mortars.

Construction of High Efficient g-C3N4 Nanosheets Combined with Bi2MoO6 Photoanodes for Dye Sensitized Solar Cells

In this study, two narrow band gap semiconductor nanomaterials, graphitic carbon nitride (g-C3N4) and Bi2MoO6, were selected and coupled to form series of g-C3N4/Bi2MoO6 photoanodes. The existence of strong interfacial interactions between g-C3N4 and Bi2MoO6 were extensively characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV–Vis diffuse reflectance spectra (UV–Vis DRS) and Photoluminescence (PL). XRD and TEM results suggest that Bi2MoO6 belongs to orthorhombic crystal structure with fiber like morphology with average diameter of 20–30 nm and length up to several micrometers. Sandwich type solar cell was fabricated by deposition the hybrid materials on FTO glass substrate and technically studied the photovoltaic (PV) parameters through J–V characteristics. The results express that g-C3N4/Bi2MoO6 hybrid photoanode show fabulous photo conversion efficiency (PCE) of (13.56%), excellent stability and reusability. The superior photovoltaic performance of g-C3N4/Bi2MoO6 nanocomposite was owing to the interface of g-C3N4/Bi2MoO6 heterostructures whereas reduced the band-gap which enables high separation efficiency, suppressed recombination rate of charge carriers and their high specific surface area (103.56 m2/g). A possible photovoltaic mechanism under sun light was systematically discussed based on the experiment results.

Preparation and measurement of properties of BiOBr/BiOCl/PANI ternary nanocomposite for highly efficient visible light photocatalytic applications

In this paper, we report the synthesis of the BiOBr/BiOCl/PANI ternary nanocomposite using a simple co-precipitation method. The modified photocatalyst produced was characterized by the FT-IR, FE-SEM equipped with EDS (as a Map), TEM, XRD, PL, Raman, and UV–Vis DRS analytical techniques. The synergetic effect of PANI and surface defects in nanoplates can prolong the recombination rate of photo-generated charge carriers. Thus, photocatalytic and photoelectrochemical activities of samples have been studied. Then, the methyl orange (MO) degradation performance of PANI/BiOBr and BiOBr/BiOCl/PANI was investigated under visible light irradiation. The lamp used to simulate sunlight in this photocatalytic study process was power down white light (5-W LED), less reported. The results got exhibited that the as-prepared BiOBr/BiOCl/PANI (90:10, Bi:PANI) nanocomposite showed a higher photocatalytic efficiency. Based on the scavenger tests, ·O2− played a significant role in the degradation of MO. The connection between BiOBr, BiOCl, and PANI improved photocatalytic activity, which enhanced migration rate of the photo-generated electrons besides limiting the recombination of photo-generated electron–hole pairs.

Silver decorated CeO2 nanoparticles for rapid photocatalytic degradation of textile rose bengal dye

High quality silver (Ag) decorated CeO2 nanoparticles were prepared by a facile one-step chemical method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), High resolution transmission electron microscopy (HR-TEM), fourier transform infrared spectrometer (FT-IR), electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), UV–Visible absorption (UV–Vis), photoluminescence (PL) and thermogravimetric analysis. The decoration of Ag on CeO2 surface was confirmed by XRD, EPR and HR-TEM analysis. Harmful textile pollutant Rose Bengal dye was degraded under sunlight using the novel Ag decorated CeO2 catalyst. It was found that great enhancement of the degradation efficiency for Ag/CeO2 compared to pure CeO2, it can be ascribed mainly due to decrease in its band gap and charge carrier recombination rate. The Ag/CeO2 sample exhibited an efficient photocatalytic characteristic for degrading RB under visible light irradiation with a high degradation rate of 96% after 3 h. With the help of various characterizations, a possible degradation mechanism has been proposed which shows the effect of generation of oxygen vacancies owing to the decoration of Ag on the CeO2 surface.

Synthesis, Characterization, and Photocatalytic Activity of g-C3N4/GaN-ZnO Composite

Recently, photocatalysis process has shown great potential as a low-cost, environmentally friendly, and sustainable method for the water/wastewater treatment. Among that, g-C3N4 is one of the most promising photocatalyst and widely used for a variety of applications. In spite of some unique features such as strong reduction ability, active under visible light, nontoxic, and high stability, g-C3N4 photocatalytic capability under visible light is limited due to fast recombination rate of reactive charges. To deal with this issue, in this study, g-C3N4 is combined with GaN-ZnO for reducing the recombination rate of charge carriers and increasing the active sites. The g-C3N4/GaN-ZnO composite was characterized by several methods such as SEM, EDX, XRD, FT-IR, UV-Vis, and BET. It is also observed that the composite with outstanding features can work effectively under visible light; thus, it is likely to be widely applied in environment treatment, especially in antibiotic residue with more than 90% of tetracycline was decomposed after 3 hours.

Effect of Ligand Functionalization on the Rate of Charge Carrier Recombination in Metal-Organic Frameworks: A Case Study of MIL-125.

Ligand functionalization is a powerful approach for modifying the electronic structure of metal-organic frameworks when targeting the optimal electronic properties for photocatalysis and photovoltaics. However, its effect on the charge carrier lifetimes and recombination pathways remains unexplored. In this work, first-principles simulations, including nonadiabatic molecular dynamics, are performed for the representative TiO2-based metal-organic framework systems MIL-125-X to unravel the impact of ligand functionalization on the nonradiative electron-hole recombination process, decoherence rates, and phonon modes giving the largest contribution to the nonradiative decay. Nonradiative recombination rates, simulated using the PBE0 density functional, are in excellent agreement with experiment. The ligand functionalization in MIL-125-X influences the recombination rates, unraveling the trend opposite to the evolution of the band gap and affecting the nonadiabatic coupling coefficients. Ligand modification impacts the phonon modes, which contribute most to the recombination process, altering the distribution between soft phonon modes and vibrational modes associated with specific structural motifs.

CdS decorated MnWO4 nanorod nanoheterostructures: a new 0D-1D hybrid system for enhanced photocatalytic hydrogen production under natural sunlight.

Constructing a heterostructure is an effective strategy to reduce the electron–hole recombination rate, which enhances photocatalytic activity. Here, we report a facile hydrothermal method to grow CdS nanoparticles on MnWO4 nanorods and their photocatalytic hydrogen generation under solar light. A structural study shows the decoration of hexagonal CdS nanoparticles on monoclinic MnWO4. Morphological studies based on FE-TEM analysis confirm the sensitization of CdS nanoparticles (10 nm) on MnWO4 nanorods of diameter-35 nm with mean length ∼100 nm. The lower PL intensity of MnWO4 was observed with an increasing amount of CdS nanoparticles, which shows inhibition of the charge carrier recombination rate. A CdS@MnWO4 narrow band gap semiconductor was employed for photocatalytic hydrogen generation from water under solar light and the highest amount of hydrogen, i.e. 3218 μmol h−1 g−1, is obtained which is 21 times higher than that with pristine MnWO4. The enhanced photocatalytic activity is ascribed to the formation of a CdS@MnWO4 nanoheterostructure resulting in efficient spatial separation of photogenerated electron–hole pairs due to vacancy defects. More significantly, direct Z-scheme electron transfer from MnWO4 to CdS is responsible for the enhanced hydrogen evolution. This work signifies that a CdS decorated MnWO4 nanoheterostructure has the potential to improve the solar to direct fuel conversion efficiency.

Sunlight-assisted degradation of textile pollutants and phytotoxicity evaluation using mesoporous ZnO/g-C3N4 catalyst.

Accessibility of adequate safe and fresh water for human consumption is one of the most significant issues throughout the world and extensive research is being undertaken to resolve it. Nanotechnology is now an outstanding medium for water treatment and remediation from microorganisms and organic dyes, as compared to conventional treatment methods. For this task graphitic carbon nitride (g-C3N4) is a potential nanomaterial for environmental remediation, but its photogenerated charge carrier recombination rate restricts its use in practical applications. Hence, in the current study, we used a simple one-step calcination method to synthesize various ratios of ZnO/g-C3N4 binary nanocomposites. The band gap of g-C3N4 is 2.70 eV, but it is shifted to 2.60 eV by the 0.75 : 1 ZnO/g-C3N4 binary nanocomposite. Moreover, phase structure, morphology, thermal stability, oxidation state, elemental analysis, and surface area were evaluated using XRD, SEM, TEM, TGA, XPS, and BET analysis. The optimal ZnO loading content was determined and the mechanism of enhanced photocatalytic activity was studied in detail. The photocatalytic efficiency of the best catalyst was employed for the degradation of textile effluent followed by phytotoxicity evaluation using methylene blue (MB), and rhodamine B (RhB) as a model substrate was tested. Furthermore, the textile effluent treatment analysis discovered that the 75 mg concentration of 0.75 : 1 ZnO/g-C3N4 catalyst degraded up to 80% within 120 min and significantly reduced the concentrations of different physico-chemical parameters of textile effluents. These treated effluents have no phytotoxic effects on fenugreek plants, according to a pot study. It was found that the mesoporous 0.75 : 1 ZnO/g-C3N4 catalyst can be used as an effective and low-cost technique for the degradation of azo dyes in textile wastewaters.

Facile synthesis of 2D nanoflakes and 3D nanosponge-like Ni1−xO via direct calcination of Ni (II) coordination compounds of imidazole and 4-nitrobenzoate: Adsorptive separation kinetics and photocatalytic removal of Amaranth dye contaminated wastewater

This study reports a simple method of direct calcination of Ni (II) coordination compounds with N-donor and O-donor ligands such as imidazole and 4-nitrobenzoate to form 2D and 3D Ni1−xO nanostructures. Controlled calcination of imidazole coordinated compound [Ni(Im)6](4-nba)2.2H2O (I) produced 2D nanoflakes in comparison to 4-nitrobenzoate coordinated compound [Ni(H2O)4(4-nba)2].2H2O which formed Ni1−xO nanosponge. Replacement of four coordinated imidazole ligands in compound I with an equivalent number of 4-nitrobenzoate and water molecules as in [Ni(H2O)2(Im)2(4-nba)2] (II) lead to the collapse of flake-like structure upon combustion with the induction of porosity, confirming the dominant effect of 4-nitrobenzoate ligand to form porous structures of Ni1−xO. Material characterization studies revealed that all Ni1−xO nanostructures exhibit cubic phase wherein increase in surface area, pore-volume, and reduction in particle size from 2D nanoflakes to 3D nanosponge is evident. The adsorptive removal of Amaranth dye as a model pollutant using synthesized Ni1−xO nanostructures exhibited high dye removal efficiency of up to 82.81% in the case of 3D nanosponge. The adsorption process is well explained based on the Sips isotherm model and pseudo-first-order reaction kinetics. Photocatalytic Amaranth dye degradation efficiency of 93.80% in 70 min with highest kapp = 4.04×10−2 min−1 is achieved which is attributed to the high surface area and reduction in charge carrier recombination rate as a result of extensive and robust mesoporous structure.

Layer-by-Layer Titanium (IV) Chloride Treatment of TiO2 Films to Improve Solar Energy Harvesting in Dye-Sensitized Solar Cells

A layer-by-layer titanium (IV) chloride treatment was applied on different layers of TiO2 in dye-sensitized solar cells (DSSCs). The effects were analysed and compared with standard untreated devices. A significant increase in short-circuit current density (JSC) was observed by employing layer-by-layer TiCl4 treatment of TiO2 in DSSCs. This increase of JSC is attributed to the increased inter-particle connectivity and increase in TiO2 nanoparticle size, resulting in better electron transfer and a lower charge carrier recombination rate. The DSSC fabricated with layer-by-layer-treated TiO2 achieved power conversion efficiency of 8.3%, which is significantly higher than the 6.7% achieved for the DSSC fabricated without TiCl4 treatment. Electrochemical impedance spectroscopy (EIS) was performed to assess the better performance of the device fabricated with TiCl4 treatment. Atomic force microscopy and surface roughness were studied to visualize and statistically determine the function of TiCl4 treatment on different layers of TiO2. Transient photocurrent and transient photovoltage measurements were also performed to gain insight into interfacial charge carrier recombination.

Size-dependent effects of ZnO nanoparticles on the photocatalytic degradation of phenol in a water solution

The effect of the ZnO nanoparticles (NPs) size on the photocatalytic degradation of phenol in a water solution under the influence of UV and Vis radiation was discussed. For the first time, research on photocatalytic degradation has used ZnO NPs produced by only one method (microwave solvothermal synthesis without heat treatment or other processes of reduction/oxidisation of the surface of NPs samples). ZnO NPs average size was determined using the Scherrer's formula, Nanopowder XRD Processor Demo web application, by converting the results of the specific surface area-density, and TEM tests. The ZnO NPs (average size between 23 nm and 71 nm) characterise by uniform morphology and narrow size distribution. The photocatalytic performance of ZnO NPs increases with the increase of the particle size and the decrease of the specific surface area. For both UV and Vis radiation, the highest reaction rate for phenol degradation was found for ZnO sample with the average particle size of 71 nm. Low concentrations of resorcine and hydroquinone (co-products of phenol degradation) were found for UV light photocatalytic test. However, high concentrations of hydro- and p-benzoquinone were observed for visible light photoactivity due to the slower decomposition of the main contamination associated with the utilized of other type of radiation. The photocatalytic activity was found to be attributable to the decrease in the charge carrier recombination rate.