Recombination Of Electron-hole Pairs Research Articles

Investigating the synergistic effect of Nd3+ and Ni2+ in CuO nanocrystals on their structural, optical, and magnetic properties for photovoltaic and photocatalytic implementations

The wet chemical precipitation technique was used to synthesize CuO, Nd:CuO and Ni-Nd:CuO nanoparticles efficiently. The produced substance was tested using X-ray diffraction (XRD) for confirming the crystallite structure, and scanning electron microscopy (SEM) was used to examine the morphological properties of the produced materials. Crystal defects and optical properties of the synthesized samples were analyzed through luminescence (PL) investigations and UV–Vis spectroscopy. EIS spectrum was utilized to study the electrochemical behavior of the prepared material. Vibrating Sample Magnetometer (VSM) was employed to examine the magnetic properties influencing from the doping of Ni2+ and Nd3+ ions into CuO, attributed to their substantial magnetic moment and ferromagnetic traits. Photovoltaic efficiency of the prepared material was studied by J-V characteristics and photon-to-electron converting efficacy (IPCE) studies. Photocatalytic properties were studied by degrading MB and RhB dyes. The enhancement in the photocatalytic performance of the Ni-Nd:CuO was a result of suppression of photogenerated electron-hole pair recombination and accelerated separation and migration of photogenerated charges.

Intercalation of novel Ocimum Sanctum leaves derived carbon dots between g-C3N4/CoFe2O4 Z-scheme heterojunction system for boosting the radicals’ generation in photo-Fenton degradation and synchronized electrochemical sensing of sulfamethoxazole antibiotic

Deeming about incessant consumption and disposal of pharmaceutical antibiotics in natural water bodies, this study demonstrates the synthesis of a novel Tulsi leaves (Ocimum Sanctum) derived carbon dots modified Z-scheme g-C3N4/CoFe2O4 heterojunction system. Characterization techniques namely XRD, FT-IR, XPS, FE-SEM, HR-TEM and EDX supported composite formation. Fabricated catalysts presented excellent photocatalytic performance towards removal of sulfamethoxazole (SMX). UV–vis DRS, PL and EIS findings suggested the augmented visible light absorption capability, suppression of electron-hole pairs recombination and effective separation of charge carriers which were accountable for degradation process. Probable mechanistic pathway for SMX removal was photo-Fenton assisted with Z-scheme separated electron-hole pairs via activation of H2O2, where hydroxyl radicals (•OH) were main reactive species. Additionally, the prepared material was employed as electrochemical sensor for individual as well as simultaneous detection of SMX and trimethoprim with quite impressive detection limits of 0.042 µM and 0.047 µM, respectively.

Structural, optoelectronic, mechanical and thermoelectric properties of ZrO2 via band engineering with Nb doping

The study investigates the structural, mechanical, optoelectronic, and thermoelectric properties of pure and doped ZrO2 using WIEN2k. The goal is to evaluate their potential contribution to future thermoelectric and photovoltaic systems. Thermodynamic stability is confirmed through molecular dynamic simulations, while mechanical stability is confirmed through mechanical features. The electronic characteristics are determined using the GGA-PBE functional. For pristine, 25 % doped, and 50 % doped ZrO2, the measured band gaps were 3.10, 2.92, and 2.73eV, respectively. Significant absorption and conductivity are found in the examined optical properties, together with decreased reflectance and optical loss, which points to a lower rate of electron-hole pair recombination. At lower temperatures, the thermoelectric properties show a noteworthy ZT. As a result, these materials may efficiently transform thermal energy into useful electrical power and offer a considerable potential for optoelectronic technology.

Fabricating FeS2/Mn0.3Cd0.7S S-scheme heterojunction for enhanced photothermal-assisted photocatalytic H2 evolution under full-spectrum light

To effectively harness solar energy, the rational construction and development of full-spectrum photocatalysts has become an appealing challenge. In this study, a novel full-spectrum responsive FeS2/Mn0.3Cd0.7S (FS/MCS) S-scheme photocatalyst was obtained by attaching FeS2 nanoparticles with excellent photothermal properties on Mn0.3Cd0.7S nanorods. The photocatalytic hydrogen production rate of the optimal FS/MCS composite was 52.017 mmol·g−1·h−1 under full-spectrum irradiation, which was 3.88 times that of pure MCS. Based on the experimental results and density functional theory (DFT) calculations, the enhanced photoactivity of FS/MCS was attributed to the synergetic effects of photothermal and S-scheme heterojunction. The photothermal effect of FeS2 could convert the near infrared light to heat, which elevated the local temperature of photocatalyst particles, thereby promoting the photocatalytic reaction. Meanwhile, the S-scheme heterojunction between FeS2 and Mn0.3Cd0.7S accelerated the charge transfer and suppressed the recombination of electron-hole pairs, thereby enabling efficient charge separation while maintaining high redox potentials. This work offers a novel perspective on constructing a full-spectrum-driven photothermal-assisted photocatalytic H2 evolution system though the dual effects of photothermal and heterojunction.

Structural and optical investigation of Nb5+-doped Sn3O4 for photoelectrochemical hydrogen production

We report herein, the microwave-assisted hydrothermal (MAH) synthesis of Nb5+-doped Sn3O4 nanoparticles for the photoelectrochemical production of hydrogen (H2). Nb5+ ions inside the Sn3O4 created structural defects, contributing to a local structural disorder, as confirmed by micro-Raman spectra. Photoluminescence spectroscopy indicated the decrease of the violet-blue–green visible emission after adding Nb5+, revealing the formation of alternative energy pathways for the electron/hole recombination. Through the morphological analysis, it was observed that the Nb5+ dopant slightly changed the morphology of nano-petals in Sn3O4. We demonstrate that the 3% Nb5+ doped-Sn3O4 photoanode presented higher charge carrier mobility, higher photocurrent density, and an impressive H2 production of 1.50 mmol L-1 in a 3 h experiment, compared to the pure Sn3O4 material. The best performance of the Nb5+ doped Sn3O4 nanomaterial could be ascribed to the formation of new energy levels in the Sn3O4 band gap, thereby inhibiting the electron-hole pair recombination and positively affecting the photoelectrochemical response of the doped material.

Facile construction of ZnWO4/g-C3N4 heterojunction for the improved photocatalytic degradation of MB, RhB and mixed dyes

This study presents the construction of binary ZnWO4/g-C3N4 nanocomposite via a facile hydrothermal approach to enhance the photocatalytic performance under the visible light irradiation. The proposed ZnWO4/g-C3N4 nanocomposite photocatalyst shows excellent photodegradation towards organic dyes, such as methylene blue (MB) and rhodamine B (RhB). The optimal loading of ZnWO4 and g-C3N4 leads to the synergistic effect which plays a predominant role in inhibiting the fast electron-hole pairs recombination rate at the interface of ZnWO4/g-C3N4 photocatalyst. The degradation rates of MB and RhB is achieved around 92.9 % and 88.8 % under the visible light irradiation for 120 min. According to our findings, the radical quenching experiments suggested that the ●OH radicals played a positive impact in the photodegradation process. Since, our proposed photocatalyst exhibit superior photocatalytic activity towards the individual MB and RhB degradation. The ZnWO4/g-C3N4 photocatalyst were further applied to demonstrate the degradation of mixed dyes (MB and RhB) at an irradiation time of 180 min. In the mixed dye solution, the ZnWO4/g-C3N4 photocatalyst achieved a highest reaction rate of 0.010 min−1 for MB and 0.012 min−1 for RhB with the degradation rate of 87.8 % and 83.3 % for RhB and MB, respectively. For the mixed dyes, the radical quenching experiments confirmed that the ●OH radicals are responsible for the fast photodegradation. Additionally, the practicality of the proposed ZnWO4/g-C3N4 photocatalyst towards the degradation of MB, RhB and the mixed dyes were examined in the tap water samples. Furthermore, the plausible photodegradation mechanism of ZnWO4/g-C3N4 photocatalyst was proposed in detail. This study provides a new insight for the simultaneous degradation of mixed chemical pollutants using our proposed ZnWO4/g-C3N4 photocatalyst.

Construction of In2S3–In(OH)3–ZnS nanofibers for boosting photocatalytic hydrogen evolution

This research involved synthesizing In2S3–In(OH)3 nanosheets through a simple hydrothermal method at a low reaction temperature. The impact of different indium chloride concentrations on the morphology and crystal structure of In2S3–In(OH)3 nanostructures was investigated. The discussion extended to the photocatalytic hydrogen evolution of both In2S3–In(OH)3 nanosheets and nanofibers. These findings indicated that In2S3–In(OH)3 nanofibers exhibited optimal photocatalytic hydrogen production at various indium chloride concentrations. Furthermore, In2S3–In(OH)3–ZnS heterostructures were created by reacting In2S3–In(OH)3 nanosheets with varying concentrations of ZnS precursors. The study delved into the morphology and crystal structure, emphasizing photocatalytic hydrogen production in In2S3–In(OH)3–ZnS nanofibers under different concentrations of ZnS precursors. Remarkably, the In2S3–In(OH)3–ZnS nanofibers demonstrated exceptional hydrogen production efficiency, attributed to their larger specific surface area, improved blue light absorption, and reduced electron-hole pair recombination. Additionally, a comprehensive analysis explored the photocatalytic reaction mechanism, pH values, sacrificial reagents, sacrificial reagent concentrations, light source types, and intensities. These results highlighted the exceptional reusability of In2S3–In(OH)3–ZnS nanofibers in photocatalytic hydrogen production, showcasing their potential for cost-effective and highly efficient applications in diverse fields.

Fabrication of sulfur doped exfoliated gCN photocatalyst for enhanced visible light degradation of pernicious organic pollutants and their photocatalytic antibacterial activity

The synthesis of sulfur-doped exfoliated graphitic carbon nitride (S-gCN) photocatalyst was achieved by the implementation of a two-step calcination technique. The XRD results revealed that all the fabricated photocatalytic materials were crystalline in nature. The inclusion of 5% sulfur in gCN led to a conspicuous escalation in the surface area of photocatalyst, rising from 10.294 to 61.185 m2g⁻1. Morphological scrutiny of the samples using FE-SEM revealed that pristine gCN exhibited tightly stacked small nanosheets, whereas inclusion of sulfur and exfoliation resulted in generation of loosely distributed large nanosheet. Furthermore, the inclusion of sulfur also induced a shift in the energy band gap (Eg) from 2.81 eV to 2.63 eV, making it felicitous for investigation as proficient visible light photocatalyst. Additionally, the photoluminescence photo-induced charge carrier recombination behavior revealed a reduced peak intensity for 5% S-gCN compared to other synthesized compositions. This observation can be directly linked to the minimized electron-hole pairs recombination during photocatalysis, underscoring its superior photocatalytic performance. Our findings revealed that the 5% S-gCN photocatalyst exhibit the most promising attributes, it degraded Tetracycline drug, Chlorpyrifos pesticide and Eriochrome Black T dye under visible light irradiation almost ∼4 times more efficiently than pristine gCN. Additionally, exceptional visible light photocatalytic antibacterial efficacy was also perceived by 5% S-gCN against S. aureus bacteria. Overall, the present research sheds light on how doping and exfoliation interact to modify the structure and catalytic properties of gCN, paving the way for the development of outstanding performance, visible light-responsive efficient photocatalysts for environmental restoration.

Creating electron traps in BiOBr nanosheet arrays by bulk-phase F doping to restrain carrier recombination for efficient photoelectrochemical water splitting system

Bismuth oxide semiconductors in the field of photoelectrochemical (PEC) water splitting face the problems of narrow photo response range and fast carrier compounding. On the basis of the above problems, we used a solvothermal method to prepare BiOBr nanosheet arrays (NSAs), which have a special structure that facilitates carrier transport. Subsequently, the F element was introduced into the bulk phase of BiOBr using a simple hydrothermal method. The results show that the BiOBr-F photoelectrode exhibits excellent photoelectrocatalysis performance under light and bias voltage. The photocurrent density of the BiOBr-F photoelectrode reached 28.35 μA cm−2 at 1.23 V vs. RHE, which is 2.01 times higher than that of the pure BiOBr, while a negative shift of the onset potential of 119 mV was obtained. The optical absorption tests show that the introduction of the F element forms an impurity energy level thereby extending the optical absorption range of BiOBr. Photoluminescence tests reveal that the introduction of F element effectively restricts the electron-hole pair recombination. This is due tothe fact that the F atoms replace some of the O atoms in BiOBr to create electron traps, thus forming a large number of electron-rich regions in the structure, which in turn reduces the electron-hole pair recombination. This work provides an effective solution to reduce the recombination between carriers by creating electron traps in semiconductor materials through bulk phase doping.

Up-conversion luminescence and Bi SPR effect promoted Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst for efficient photocatalytic hydrogen production with simultaneous degradation of malachite green

Photocatalytic hydrogen production with simultaneous degradation of organic pollutants by using solar energy provide a promising strategy to solve the energy and environmental issue in the future. However, for onefold wide band-gap semiconductor, the poor photocatalytic efficiency limits its application on a large scale due to its easy recombination of photo-generated electron-hole pairs and low solar energy utilization. Herein, a novel Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst is prepared via photo-assisted isoelectric point method. In this composite photocatalyst, up-convention luminescence material, NaYF4:Er,Yb,Tm, can offer more ultraviolet light and visible light to intensify the activations of BiOBr and metal Bi nanoparticles, respectively. Furthermore, the formation of Z-scheme BiVO4(040)-BiOBr photocatalystic sytem, the spatial separation of the BiVO4(040) and BiVO4(110) facets and the presence of metal Bi surface plasmon resonance effect are contributed to the high-efficiency separation of the photo-generated electron-hole pairs. The experimental results show that as-prepared Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst exhibits advanced photocatalytic hydrogen production amount (192.0 μm) and excellent degradation ratio of malachite green (88.51 %) under simulated sunlight irradiation for 5.0 h. The apparent quantum yield of the Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst at 420 nm reaches a specific value of 5.8 %. In addition, Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst also remains a high stability in the photocatalytic hydrogen production with simultaneous degradation of malachite green within six reuse. At last, the possible reaction mechanism and degradation pathways of malachite green caused by Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst under simulated sunlight irradiation are put forward.

A sandwich-type photoelectrochemical biosensor based on anthocyanin-sensitized ZnO/P5FIn heterojunction for the sensitive detection of CYFRA21-1.

. A sandwich-type photoelectrochemical (PEC) immunosensor based on a ZnO/poly(5-formylindole) (P5FIn)/anthocyanin heterostructure was developed to achieve sensitive background-free detection ofthe tumor marker CYFRA21-1. ZnO with good photovoltaic properties is combined with narrow bandgap P5FIn to form a p-n type heterojunction. This structure reduces the electron-hole pair recombination, thereby enhancing the photocurrent response of the composite. Anthocyanidins are environmentally friendly natural compounds with excellent antioxidant, redox properties, and remarkable electrochemical activity. After sensitization by anthocyanins, the absorption and utilization of visible light in the composites are enhanced, further improving the PEC luminescence efficiency of the materials. Additionally, boron nitride quantum dots (BN QDs) are combined with Ab2 via polydopamine (PDA) as a secondary antibody marker, enhancing its sensitivity. The biosensor exhibited a linear detection range of 0.001-100ngmL-1 with a limit of detection (LOD) of 0.00033ngmL-1. Furthermore, this biosensor demonstrates excellent selectivity, reproducibility, and stability, as well as successful results in analyzingactual human serum samples. This approach provides a feasible method for tumor marker detection.

(Ce, Nd) co-doped TiO2 NPs via hydrothermal route:Structural, optical, photocatalytic and thermal behavior

Rare earth (Ce, Nd) doped/co-doped titania (TiO2) nanoparticles were successfully produced by hydrothermal route. Titanium isopropoxide (IV), cerium nitrate hexahydrate and neodymium nitrate hexahydrate were utilized as raw/starting materials. The effect of Ce and Nd doping/co-doping in TiO2 were studied through different complementary tools such as XRD, FTIR, FE-SEM, EDX, XPS, UV–Visible, PL, photocatalytic and thermal analysis. XRD spectra revealed anatase tetragonal phase and cubic phase due to titania and ceria nanoparticles respectively. The crystallite size, lattice constants, volume and no. of unit cell were determined through XRD data. Optical studies revealed the band gap, urbach energy, extinction coefficient, refractive index, optical conductivity and photoluminescence emission wavelength. FTIR spectra investigated the chemical bondings and functional groups present in prepared samples. Optical absorption spectra confirmed that absorption edge is red shifted, indicating a decrease in band gap from 3.5 to 3.0 eV with the incorporation of rare earth ions (Ce, Nd) in TiO2 matrix. The rate of electron-hole pair recombination was reduced through co-doping of (Ce, Nd) in TiO2 lattice as exhibited by reduction in intensity of photo luminescence spectra. The photocatalytic efficiency was enhanced with the integration of rare earth metal ions in TiO2 matrix for different dyes such as rhodamine B (RhB) and malachite green (MG) with visible light irradiation. The degradation efficiency of (Ce, Nd) co-doped TiO2 NPs against RhB and MG dyes was found to be 89 and 95 % respectively. TGA analysis was carried out to find weight loss during different thermodynamic phases such as dehydration, decomposition and combustion, and crystallization. Various thermodynamic parameters such as activation energy, entropy and enthalpy were estimated by thermal analysis.

Ordered porous carbon nitride embedded with truncated carbon nanotubes for boosting photocatalytic degradation

Limited light absorption and low charge separation rates are the main obstacles for graphitic carbon nitride-based photocatalysts. In terms of these defects, an ordered-porous graphitic carbon nitride composites (PCN@CNT) modified with truncated carbon nanotubes (CNTs) were composited through hydrothermal-calcination method in this work. Due to their electron trapping ability, the CNTs can enhance visible light absorption, narrow the bandgap, and act as electron concentrators, achieving that spatial separation of photogenerated carriers can inhibit electron-hole pair recombination efficiently. In addition, a controllable ordered-porous structure was constructed to provide abundant active sites and mass transfer channels, shortening the carrier migration path. These two modifications acted synergistically to enhance the catalysts' performance. The top-performing sample in this work, PCN@CNT-1, showed significant improvement in photovoltaic performance and achieved a 97.7 % degradation of rhodamine B, with a photocatalytic degradation rate constant (k-value) more than three times that of PCN. This work demonstrates the potential for modification by coupling CNTs to design carbon-nitride-based photocatalysts with excellent catalytic performance, which can be used as catalysts for wastewater purification.

Photolysis and photocatalysis of methylene blue by graphene oxide nanoparticle under sunlight irradiation

The Hummer technique was utilised to produce graphene oxide (GO), for this research. X-ray diffraction (XRD), energy dispersive X-ray (EDX), and a field emission scanning electron microscope (FESEM) were used to examine the structural properties of GO nanoparticles.By boosting adsorption, expanding the light absorption range, and blocking electron-hole pair recombination, GO enhances the photocatalytic efficiency. The GO have enormous potential uses in the degradation of organic contaminants from wastewater, and their manufacturing is expected to be scalable using this simple process. The improved catalytic activity of GO nanoparticle has been linked to the greater adsorption susceptibility of dye molecules, high charge separation, and suppressed recombination of photogenerated electron-hole pairs brought about by the presence of GO. These results demonstrated the promising prospects for future use of graphene-based semiconductor nanocomposites as visible-light photocatalysts in the field of water purification.

Direct Z-scheme ZnS/HfS2 heterojunction for photocatalytic overall water splitting with high carrier mobility

The electronic and photocatalytic properties of a type-II ZnS/HfS2 heterojunction are comprehensively analyzed through first-principles calculations in this paper. By calculating the binding energy and phonon spectrum of five potential stacking patterns, the stable structure of the ZnS/HfS2 heterojunction is determined. The electronic structure calculations indicate that the heterojunction has a type-II alignment with a 1.26 eV band gap. The heterojunction exhibits high carrier mobilities (4387.36 and 9561.39 cm2V–1S−1 for X and Y directions). The photocatalytic water splitting process of the heterojunction can be explained by the direct Z-scheme mechanism. The built-in electric field enables rapid recombination of electron-hole pairs at CBM and VBM, while the hydrogen evolution reaction and oxygen evolution reaction can separately be achieved at the ZnS layer and HfS2 layer to complete the overall water splitting. The free energy analysis indicates that the ZnS/HfS2 heterojunction has high activity for overall water splitting under illumination. Moreover, the calculated solar-to-hydrogen efficiency of the heterojunction reaches 30%, ensuring its photocatalytic performance. Remarkably, the type-II alignment is maintained and the catalytic performance can be further improved under biaxial strain because of the enhanced optical absorption in visible light and the reduced band gap. This work reveals that ZnS/HfS2 heterojunction is a potentially novel photocatalytic material for efficient overall water splitting.

Chemical-Free Stable and Multifunctional Electro-Based System for Treatment of Pesticides from Aqueous Solution

The usage of pesticides has become a common practice in modern agricultural systems to meet the growing demand for food production. However, the uncontrolled use of such chemicals results in the deterioration of natural ecosystems and living beings. Thus, herein, a hybrid treatment system performing the combined functions of electro- and photo Fenton was designed to treat aqueous pesticide solution. The anode was comprised of metal oxide-based electrode (MOx), whereas the cathode was comprised of N-doped carbon electrode (N-C). Both the electrodes consist of light-responsive photocatalysts, which facilitates the removal of pollutants by generating reactive radical species such as OH• and O2 •-. The application of external anodic bias helps to improve the photocatalytic activity by preventing the recombination of electron-hole pairs. In addition, N-C on the cathode helps to catalyze the reduction of O2 to H2O2, which further reacts with Fe2+ in the system to initiate the Fenton reaction. The hybrid reactor was further optimized to study the underlying mechanisms by varying the experimental conditions such as pH, current density, electrolyte concentration, and external H2O2 concentration.Moreover, scavenging tests were performed using methanol and tertbutyl alcohol to identify the predominant radical species responsible for removing pollutants from the aqueous solution. Also, the reusability test showed that the prepared electrodes were stable for more than three successive cycles, thus offering sustainability. In general, the present study demonstrates the potential of hybrid treatment units for environmental applications and acts as a stepping stone for future endeavors in material synthesis and sustainable treatment solutions.

A comprehensive study of laser irradiated hydrothermally synthesized 2D layered heterostructure V2O5(1−x)MoS2(x) (X = 1–5%) nanocomposites for photocatalytic application

Abstract It has been studied that both two-dimensional (2D) MoS2 and V2O5, which are classified as transition metal dichalcogenides and transition metal oxides, are good photocatalyst materials. For this purpose, the hydrothermal method was practiced to synthesize V2O5(1−x)MoS2(x) (X = 1–5% w/w) nanocomposites with different 1–5% w/w weight percent of MoS2 as a prominent photocatalyst under laser irradiation for 2, 4, 6, 8, and 10 min to tune photocatalytic degradation of industrial wastage water. The surface of the 2D molybdenum nanolayered matrix was efficaciously decorated with V2O5 nanoparticles. The crystal phase and layered structures of the V2O5(1−x)MoS2(x) (X = 1–5% w/w) nanocomposites samples were verified by X-ray diffraction and scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy respectively. In the range of the UV visible spectrum, the increment in light absorption from 3.6 to 14.5 Ω−1 cm−1 with an increase of active surface from 108 to 169 μ m 2 {{\rm{\mu }}{\rm{m}}}^{2} with increased MoS2 doping percentage. Furthermore, dielectric findings like the complex dielectric function, tangent loss, electrical conductivity, quality factors, and impedance of V2O5(1−x)MoS2(x) (X = 1–5% w/w) nanocomposites are studied. According to photoluminescence studies, the intensity of peaks decreases when laser irradiation time and doping percentages of MoS2 are increased. As a result, a small peak indicates a decrement rate of electron–hole pair recombination, which increases the capacity for separation. Thermo-gravimetric analysis and differential thermal analysis results revealed that weight loss decreased from 0.69 to 0.35 mg and thermal stability increased with increased doping concentrations. Methylene blue was degraded in 150 min, proving that the prepared MoS2-doped V2O5 material was a stable and economically low-cost nanocomposite for photocatalytic activity.

Construction of nanocomposite hydrogel by TiO2-carbon quantum dots encapsulated in alginate with a highly efficient adsorption and photodegradation of dye pollutants

This presentation introduces an integrated photocatalyst/adsorbent system, achieved through immobilization and encapsulation of the TiO2 doped with CQDs (carbon quantum dots) nanocomposite within the calcium alginate (CaAlg) matrix. The nanoparticles and nanocomposites were analyzed using various techniques, including FE-SEM, EDX, TEM, XRD, PL, FT-IR, BET, and UV–vis DRS, to determine their structure and properties. The TiO2/CQDs/Alg nanocomposite hydrogel considerably influenced the adsorption and photocatalytic degradation of methylene blue (MB) as a dye pollutant. The adsorption studies were conducted to assess parameters such as adsorption capacity, kinetic behavior, and adsorption isotherms. The outcomes revealed a high adsorption capacity (44.13 mg/g at 90 min) and indicated that the pseudo-second-order kinetic model was highly suitable for describing the adsorption behavior of MB. Moreover, the Freundlich isotherm exhibited better fitting capabilities compared to the Langmuir isotherm. CQDs not only facilitated the transfer of photoelectrons from the TiO2 surface, preventing recombination of electron-hole pairs but also enhanced visible light absorption by the upconversion photoluminescence. The TiO2/CQDs/Alg displayed excellent photodegradation performance (97 %) of MB compared with TiO2 and TiO2/CQDs under visible light due to the abundance of active sites for MB adsorption and photocatalytic reactions. The TiO2/CQDs/Alg hydrogel exhibited excellent reusability in degrading MB for up to five consecutive cycles and showed significant swelling behavior across a broad pH range, reflecting the hydrogel's exceptional stability. The use of charge carrier scavengers indicated that O2˙−radicals were the primary surface species involved in the photodegradation of MB.

Constructing potassium and hydroxyl co-doped dual-dipole structures on highly active 3D g-C3N4 surfaces for highly boosting photocatalytic hydrogen peroxide production efficiency in pure water

Producing hydrogen peroxide (H2O2) through visible-light-driven photocatalytic oxygen reduction in pure water is crucial for sustainable ecological applications but poses significant challenges. These include the rapid recombination of electron-hole pairs and a scarcity of effective catalytic sites, which traditionally limit the process efficiency. To address these issues, we have developed a novel catalyst, designated as KCNOH, which consists of a three-dimensional (3D) porous g-C3N4 framework doped with potassium (K+) and modified with surface hydroxyl groups (-OH). This design significantly enhances H2O2 yield, achieving 91.36 μmol g-1 h-1 (cut 420 nm)—a yield approximately 36 times higher than conventional bulk g-C3N4 (2.57 μmol g-1 h-1). The introduction of a 3D porous structure provides an abundance of active-sites. The dual-dipole mechanism, facilitated by K+ ions and hydroxyl groups, plays a pivotal role by efficiently transporting photogenerated electrons and consuming holes, respectively. Through density functional theory (DFT) calculations, the changes in the band structure of the catalyst caused by the doping of potassium and the grafting of hydroxyl groups were elucidated. In addition, the transition state affinity of oxygen induced by the -OH group was also studied to reveal the synergistic catalytic mechanism. This mechanism markedly reduces carrier recombination and accelerates charge migration, underscoring its importance in catalyst design. Our findings not only improve the understanding of charge dynamics but also open novel perspectives for the design of highly-efficient composite materials, crucial for energy and environmental applications.

Enhanced Photocatalytic Degradation by the Preparation of a Stable La-Doped FeTiO3 Photocatalyst: Experimental and DFT Study.

The rapid photocarrier recombination limits the photocatalytic activity of iron titanate (FeTiO3) to be further improved. Developing novel approaches to inhibit the rapid recombination rate of the FeTiO3 photocatalysts is crucial for efficiently degrading pollutants in wastewater. Rare earth ions, with unique electron dispositions and large ion radii, could effectively inhibit photocarrier recombination. Herein, novel lanthanum (La)-doped FeTiO3 photocatalysts were designed and successfully synthesized. The photocatalytic performance of the 12 mol % La/FeTiO3 photocatalyst was superior in degrading tetracycline hydrochloride (TCH), methylene blue (MB), and brilliant blue (BB). These degradation rate constants (k) were 0.12358, 0.01357, and 0.03064 L mg-1 min-1, respectively, which were 12.83, 1.61, and 7.78 times that of pure FeTiO3. The photoelectronic tests and density functional theory (DFT) calculations revealed that the La 4f orbital forms an impurity energy level in the conduction band of FeTiO3. This level narrows the bandgap and acts as an electron acceptor, capturing photoexcited electrons and inhibiting the rapid recombination of photoexcited electron-hole pairs in FeTiO3. This work enhances the potential of FeTiO3 in the photocatalysis field and provides important insights into the efficient degradation of organic pollutants in wastewater.