Browsing by Subject "Photocatalysis"

Now showing 1 - 20 of 36

Embargo
A machine learning approach for the estimation of photocatalytic activity of ALD ZnO thin films on fabric substrates
(Elsevier, 2024-02-01) Akyıldız, Halil I.; Yiğit, E.; Arat, A. B.; Islam, S.
Research in the field of photocatalytic wastewater treatment is striving to enhance catalyst materials to achieve high-performance systems. A promising approach to this goal has been immobilizing photocatalytic materials on fibrous substrates via atomic layer deposition (ALD). Nevertheless, both the ALD process and the assessment of photocatalytic performance involve a multitude of parameters necessitating thorough investigation. In this study, we employ popular machine-learning algorithms, including Support Vector Regression (SVR) and Artificial Neural Networks (ANN), to predict the photocatalytic activity of ALD-coated textiles. The photocatalytic activity is evaluated through methylene blue and methyl orange degradation tests. Machine learning algorithms are tested and trained using the k-fold cross-validation technique. The findings demonstrate that the ANN and SVR methods utilized in this research can predict catalytic activity with mean absolute percentage errors (MAPE) of 2.35 and 3.25, respectively. This study illuminates that, within the defined range of process parameters, the photocatalytic activity of ALD-coated textiles can be precisely estimated with suitable machine-learning algorithms.
Open Access
Bi2O3 and BiOCl electrospun nanosheets and morphology-dependent photocatalytic properties
(Royal Society of Chemistry, 2014) Babu, V. J.; Bhavatharini, R. S. R.; Ramakrishna, S.
BiOCl and Bi2O3 nanosheet like structures were produced by electrospinning. The morphological changes were observed by changing precursor (BiOCl3 and Bi(NO3)3·5H 2O) concentrations. These nanosheets were analyzed by XRD, which reveals that the crystal structures of BiOCl and Bi2O3 belonged to tetragonal and beta-phase systems respectively. Both nanostructures were employed for the photodegradation of Alizarin Red S (ARS) dye under UV light (<390 nm) irradiation. BiOCl nanosheet like structures exhibited superior photocatalytic activity (PCA) for the degradation of ARS dye and their half-life was estimated from the kinetic plots of PCA. A plausible reaction mechanism is proposed for the PCA and discussed in detail. © the Partner Organisations 2014.
Open Access
Catalysis with engineered Prussian blue analogues under external bias, light, and magnetic field
(2022-07) Oglou, Ramadan Chalil
The design of robust and feasible catalysts is one of the main concerns towards a carbon emission-free world. Prussian blue analogues (PBAs), the most well-known family of cyanide-based compounds, offer diversity and facile tunability of the structural components to achieve robust catalysts with high selectivities and reproducibilities. Herein this thesis, the catalytic performances of CoFe PBAs have been investigated for glucose and water oxidation processes. The structure of the Prussian blue (PB) framework has been engineered to tune the morphological and electronic properties for enhanced catalytic activity. In this regard, my thesis could be divided into three sections: (i) Electrocatalytic glucose oxidation: In the first part of this study, a CoFe PB modified fluorine-doped tin oxide (FTO) electrode, which is prepared via an electrodeposition method, was investigated as a non-enzymatic glucose sensor under neutral conditions. The electrode exhibits a linear detection of glucose in the 0.1 − 8.2 mM range with a detection limit of 67 μM, and a sensitivity of 18.69 mA mM−1 cm−2. Its stability is confirmed with both electrochemical experiments and characterization studies performed on the pristine and post-mortem electrodes. We also conducted a comprehensive electrochemical analysis to elucidate the identity of the active site and the glucose oxidation mechanism on the PB surface. In the second part, a series of PB modified carbon cloth (CC) electrodes were prepared with different cyanoferrate groups. A sensitivity as high as 145.43 μA mM−1 cm−2 in a 0.1 – 6.5 mM concentration range is achieved with a response time below 2 s under physiological pH. The electrodes exhibit a superior selectivity of glucose in the presence of interfering agents, including sucrose, lactose, sodium chloride, ascorbic acid, and uric acid. The electrodes also show outstanding long-term stability over 15 days. Furthermore, we performed comprehensive electrochemical and characterization studies to elucidate the role of the cyanoferrate group on the morphologic and electronic properties of non-enzymatic glucose sensors. (ii) Photocatalytic water oxidation: We present a simple and easy-to-scale synthetic method to plug common organic photosensitizers into a cyanide-based network structure for the development of photosensitizer-water oxidation catalyst (PS−WOC) dyad assemblies for the photocatalytic water oxidation process. Three photosensitizers, one of which absorbs red light similar to P680 in photosystem II, were utilized to harvest different regions of the solar spectrum. Photosensitizers are covalently coordinated to CoFe PB structures to prepare PS-WOC dyads. All dyads exhibit steady water oxidation catalytic activities throughout a 6 h photocatalytic experiment. Our results demonstrate that the covalent coordination between the PS and WOC groups enhances not only the photocatalytic activity but also the robustness of the organic PS group. We find that the photocatalytic activity of these “plug and play” dyads relies on several structural and electronic parameters, including the position of the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the PS with respect to the HOMO level of the catalytic site, the intensity and wavelength of the absorption band of the PS, and the number of catalytic sites. (iii) Intermetallic charge transfer induced electrocatalysis: We report a novel route to enhance the sluggish kinetics of oxygen evolution reaction (OER) by manipulating the intermetallic charge transfer (IMCT) of PBAs. It is found that CoFe PBAs with dissimilar charge transfer abilities reveal a positive response for OER under external stimuli such as magnetic field and light illumination, in which the magnitude of enhancement can be correlated to the intensity of metal-to-metal charge transfer (MMCT) profiles rather than the catalytic activity. An enhancement of almost 57% for OER activity is observed under a 1 h light irradiation for the CoFe PBA that exhibits the strongest IMCT nature. Several control experiments are conducted correlating the direct relation of IMCT and external stimuli induced activity involving –electrochemical experiments at varying pH conditions. Overall, this thesis indicates that CoFe PBAs could be engineered to design robust catalysts for oxidation reactions. Furthermore, they could also be fine-tuned to develop catalytic assemblies, which are responsive to applied bias, magnetic field, and light irradiation. Given the previous efforts in employing PBAs for catalytic applications, this thesis pushes the limits one step forward and brings a new level to this challenge.
Open Access
Comparative study of optically activated nanocomposites with photocatalytic TiO2 and ZnO nanoparticles for massive environmental decontamination
(S P I E - International Society for Optical Engineering, 2007) Tek, S.; Mutlugun, E.; Soganci, I. M.; Perkgoz, N. K.; Yucel, D.; Celiker, G.; Demir, Hilmi Volkan
Nanocomposites that incorporate TiO2 and ZnO nanoparticles separately in three-dimensional solgel matrices through full chemical integration are prepared to perform highly efficient photocatalytic activities for applications of environmental decontamination. Spectral responses of photocatalytic TiO2 and ZnO nanoparticles exposed to UV activation for self-cleaning process were obtained as also their optical relative spectral efficiency curves from 270 to 370 nm in the UV regime. Our investigations of the optimal conditions to increase their spectral photocatalytic efficiencies resulted in remarkably high levels of optical recovery and efficiency.
Open Access
Concentrated solar radiation promoted unconventional greener approach: Solvent-free benign synthesis of functionalized benzimidazoles
(Arkat, 2018) Harsh, S.; Yusuf, M.; Sharma, R.; Kumar, Y.; Kumar, R.
Renewable concentrated solar-radiation (CSR) offered a promising en route for the development of practical, highly efficient, scalable, catalyst free and solvent-free clean process leading to the synthesis of functionalized benzimidazoles. Developed protocol has a very good substrate scope, involves mild reaction conditions and products obtained in good to excellent yields. Method presented the observations in which light alone could affect the remarkable changes with more than 85% energy saving and 75% less reaction time in listed organic transformations.
Open Access
Controlled modulation of 1D ZnO nano/micro structures: Evaluation of the various effects on the photocatalytic activity
(Elsevier Ltd, 2017) Arslan, O.; Abalı, Y.
Effects of the concentration, temperature and precursor type on the fabrication of the elongated ZnO nano/micro structures were comprehensively investigated. Analytical investigations such as SEM and statistical analysis of the elongated ZnO nano/micro structures provided wide information about the growth behavior and final geometries. Different temperatures for the 1 D ZnO formation clearly revealed that hexagonally grown ZnO nanorods were obtained. Especially low crystal diffraction characteristics at low temperature (55 °C) implied that ZnO nano/micro rod formation requires some minimum conditions for the formation of an efficient photocatalyst. All XRD investigations together with SEM and TEM supported the ligand ordered elongation conducted by diverse beginning concentrations. Since temperature found as a highly dominant actor for morphology and surface sequence as manifested in crystallinity, morphology and photocatalytic results, we have systematically summarized the growth conditions of the ZnO nano/micro rods from same precursor. © 2017 Elsevier Ltd
Embargo
Effect of optical and electronic structure on the photocatalytic activity of Al doped ZnO ALD thin films on glass fibers
(Elsevier BV, 2024-07-25) Güleç, Sena; Arat, Asife B.; Islam, Shafiqul; Akyıldız, Halil I.
Photocatalytic water treatment can be promising for eliminating toxic pollutants via a more sustainable approach using renewable sources. However, the technique still requires materials design to optimize/maximize the performance of the photocatalytic materials. Immobilizing the thin film photocatalytic materials onto high surface area textile substrates via atomic layer deposition (ALD) can offer a practical design approach. Al-doped ZnO (AZO) ALD films are deposited onto glass fabric substrates, and their photocatalytic performances were investigated in relation to the FESEM, XRD, XPS, UV-Vis, and PL characterizations. The amount of Al and the post-deposition annealing changed the materials structure, thus the photocatalytic activity of the films. Maximum performance was achieved with the 20 % Al-doped ZnO films after a post-deposition thermal annealing step at 450 degrees C. The sample also showed the highest UV-Vis absorption and PL emission among the samples. However, this sample didn't show any crystal peaks in the XRD analysis. Furthermore, the charge carrier concentrations and the mobility of the films were investigated via Hall-Effect, which showed that the 20 % AZO sample has very different features with a p-type nature compared to the other AZO films.
Open Access
Electrocatalytic water splitting with Prussian blue analogues under external stimuli
(2023-09) Ahmad, Waqar
The development of long-lasting and efficient catalysts for water splitting is crucial for the advancement of a carbon emission-free world. A well-known class of compounds called Prussian blue analogues (PBAs) offers several advantages such as high stability, diversity, and simple synthesis for the development of sustainable water-splitting devices. This thesis investigates the construction of PBA-based overall water-splitting electrolytic cells assisted with external stimuli. Alsac et al. investigated the oxygen evolution reaction (OER) efficiency of various PBAs and concluded that Co-Co exhibits the best performance as an OER catalyst among the Co-M PBAs. Ahmad et al. studied the hydrogen evolution reaction (HER) performance of various PBAs and observed that Co-Ni stands out in performance. Furthermore, Chalil Oglou et al. elucidated the effect of the magnetic field on the OER catalytic activity of Co-Fe PBA electrodeposited on the surface of the FTO. His findings unveiled an enhanced catalytic activity under the influence of a magnetic field. To further explore these concepts, we aim to move one step ahead and combine all these studies to investigate overall water splitting (OWS) under the influence of magnetic field and solar light irradiation. In this thesis, [Co-Co] was used for the OER reaction, while [Co-Ni] was utilized for the HER reaction. Both electrodes were prepared involving a two-step electrodeposition method and comprehensively characterized with SEM, EDAX, P-XRD, XPS, and ATR-FTIR. SEM images unveiled threat-like and needle-like grown particles with uniform sizes of 1-2 µm for [Co-Co] and [Co-Ni] formed on the fluorine-doped tin oxide (FTO) electrode respectively. The oxidation states of the pristine and post-catalytic electrodes and the stability during the electrocatalytic process were confirmed with XPS and FTIR studies. The electrochemical characterization of these catalysts was thoroughly investigated with linear sweep voltammetry (LSV), chronoamperometry (CA), and cyclic voltammetry (CV) profiles. The electrochemical performance was investigated in three chapters; OER, HER, and overall water splitting under magnetic and solar light irradiation. (i) OER performance of FTO/[Co-Co] was evaluated with LSV, which shows prominent enhancement peaks under the influence of external stimuli. Under the influence of the magnetic field, it illustrated an enhancement of 11.9% with an overpotential of 949 mV, while in the presence of solar light, it showed an augmentation of 10.7% with an overpotential of 949 mV. CA profiles, recorded under magnetic field showed that there is a direct relation between magnetic field strength and the enhancement in the current density. On the contrary, an opposite trend is observed with the CA profiles under solar light irradiation, which suggests that the origin of the enhancement under the magnetic field is different from the one under solar light irradiation. (ii) Similar to OER studies, HER activity of FTO/[Co-Ni] was investigated under the effect of solar light irradiation and magnetic field. The LSV profile showed enhancement only in the case of solar light, while no significant enhancement was observed under the magnetic field, contrary to the previous studies. Similar to OER, the CA profiles of FTO/[Co-Ni] illustrated the opposite trend with respect to overpotential applied. In the case of HER, CA under a magnetic field showed a small enhancement (1.4%) with an overpotential of 300 mV, which was attributed to the magnetohydrodynamic effect. (iii) Two and three-electrode systems were used to conduct the investigation into overall water splitting. To achieve a current density of 1 mA/cm2 in the two-electrode having FTO/[Co-Co] on the working/working sense electrode (W/WS) and FTO/[Co-Ni] on the counter/reference electrode R/C configuration, the system required an overpotential of roughly 1013 mV. The subsequent analysis of each electrode's unique voltage contributions helped explain this observation. OER takes around 1.3 V while it is 0.6 V for the HER side. On the other hand, in the three-electrode configuration, the working electrode was FTO/[Co-Co], the counter electrode was FTO/[Co-Ni], and the reference electrode was Ag/AgCl. The observed profile notably showed significant improvement seen when solar light and magnetic fields were present. Overall, this study indicates that there is still plenty of room for enhancement in catalysis, with slight modification in reaction conditions from another perspective i.e., external stimulus. This thesis takes a progressive step by raising the bar and adding a new dimension to the challenge of using PBAs in catalytic applications, building on earlier efforts.
Open Access
Electrospun BiOI nano/microtectonic plate-like structure synthesis and UV-light assisted photodegradation of ARS dye
(Royal Society of Chemistry, 2014) Babu, V. J.; Bhavatharini, R. S. R.; Ramakrishna, S.
BiOI electrospun nanofibers were prepared by using PAN as a supporting polymer. Subsequent annealing at 500 °C for 5 h, with a ramp rate of about 5 °C min-1 in air, breaks the nanofibers down to tectonic plate-like nano/microstructures. The surface physical and chemical structural changes were then further characterized by FE-SEM, TEM, XRD and XPS. The results reveal that the morphology and crystallite size of BiOI vary strongly depending on the precursor concentration used in the synthesis method. These nanostructures were later employed for photocatalytic degradation of a synthetic textile dye, Alizarin Red S (ARS). The photocatalytic efficiencies were found to be about 93.34% after 100 min of UV-light (340 nm) illumination. Photocatalytic activity (PCA) performance depends on morphology and band alignment. All the compositions follow first order pseudo-kinetics, which was found to be 0.1197 min-1 for a doping concentration of 3%. The enhancement in photodegradation could be possibly by photocatalysis and a photosensitization phenomenon. This has been explained based on the band edge position. © the Partner Organisations 2014.
Open Access
Electrospun Fe2O3 entrenched SiO2 supported N and S dual incorporated TiO2 nanofibers derived from mixed polymeric template/surfactant: enriched mesoporosity within nanofibers, effective charge separation, and visible light photocatalysis activity
(American Chemical Society, 2019) Pradhan, Amaresh C.; Uyar, Tamer
The α-Fe2O3 promoted and SiO2 supported N and S dual incorporated TiO2 nanofibers (FeSiNST NFs) along with neat oxide NFs have been synthesized by electrospinning via sol–gel. The keen approach is that mixed polyvinylpyrrolidone (PVP) as template and cetyltrimethylammonium bromide (CTAB) as surfactant are responsible for the creation of mesoporosity within NFs. The photoluminescence (PL) spectrum and UV–visible diffuse reflectance spectroscopic (DRS) result revealed the role of α-Fe2O3 as catalytic promoter in FeSiNST NFs by suppressing electron–hole (e––h+) recombination, red shifting, and oxygen vacancies (Ovs). The design of FeSiNST NFs by combining with SiO2 as catalytic support and N and S as visible light absorbers in TiO2, beautifies the present study. The high photocurrent (3.2 mA/cm2), high Efb value (−1.0 V), and low Rct value (∼74 Ω) support the enhanced photocatalysis (photoreduction and photodegradation) by FeSiNST in visible light. Charge transfer phenomena, Ovs, mesoporosity, and separation of e––h+ are the vital factors for an effective photocatalysis achievement.
Open Access
Enhanced photocatalytic activity of homoassembled ZnO nanostructures on electrospun polymeric nanofibers: a combination of atomic layer deposition and hydrothermal growth
(Elsevier, 2014) Kayaci, F.; Vempati S.; Ozgit Akgun, C.; Bıyıklı, Necmi; Uyar, Tamer
We report on the synthesis and photocatalytic activity (PCA) of electrospun poly(acrylonitrile) (PAN) nanofibrous mat decorated with nanoneedles of zinc oxide (ZnO). Apart from a detailed morphological and structural characterization, the PCA has been carefully monitored and the results are discussed elaborately when juxtaposed with the photoluminescence. The present hierarchal homoassembled nanostructures are a combination of two types of ZnO with diverse optical qualities, i.e. (a) controlled deposition of ZnO coating on nanofibers with dominant oxygen vacancies and significant grain boundaries by atomic layer deposition (ALD), and (b) growth of single crystalline ZnO nanoneedles with high optical quality on the ALD seeds via hydrothermal process. The needle structure (~25. nm in diameter with an aspect ratio of ~24) also supports the vectorial transport of photo-charge carriers, which is crucial for high catalytic activity. Furthermore, it is shown that enhanced PCA is because of the catalytic activity at surface defects (on ALD seed), valence band, and conduction band (of ZnO nanoneedles). PCA and durability of the PAN/ZnO nanofibrous mat have also been tested with aqueous solution of methylene blue and the results showed almost no decay in the catalytic activity of this material when reused.
Open Access
Fast and quick degradation properties of doped and capped ZnO nanoparticles under UV-Visible light radiations
(Elsevier Ltd, 2016) Mittal, M.; Sharma, M.; Pandey, O. P.
Undoped and Manganese (Mn) doped zinc oxide (ZnO) (Zn1- xMnxO, x=0.005, 0.01, 0.015 and 0.02) nanoparticles (NPs) capped with (1.0%) Thioglycerol (TG) has been successfully synthesized by co-precipitation method. Optical and morphological studies have been done for photophysical and structural analysis of synthesized materials. The photocatalytic activity of undoped and Mn doped ZnO NPs were investigated by degradation of crystal violet (CV) dye under UV-Visible light radiations. It has been found that Mn (1.0%) doping concentration is optimal for photophysical and photocatalytic properties. When the pH of as synthesized optimum doped ZnO NPs varied from natural pH i.e. from 6.7 to 8.0 and 10.0, the degradation of CV dye increases from 92% to 95% and 98% in 180min respectively. Further on increasing the pH of optimum doped synthesized NPs to 12.0, almost 100% degradation has been achieved in 150min. Optimum doped photocatalyst synthesized at pH-12.0 has also effectively degraded the CV dye solution in acidic and basic medium thus showed its utility in various industries. However, it has been found that 100% of CV dye quickly degraded in 30min when only 1.0% of hydrogen peroxide (H2O2) was introduced along with optimized NPs synthesized at pH-12. Kinetic studies show that the degradation of CV dye follows pseudo first and second-order kinetic law. Further an industrial anionic polyazo Sirius red F3B (SRF3B) dye has been degraded to 100% with optimized NPs synthesized at pH-12.0 in 15min only.
Open Access
Flexible organic-inorganic core-shell nanofibers by electrospinning and atomic layer deposition
(CRC Press, 2012) Kayacı, Fatma; Çağla, Özgit-Akgün; Dönmez, İnci; Bıyıklı, Necmi; Uyar, Tamer
Organic-inorganic core-shell nanofibers were fabricated by combining electrospinning and atomic layer deposition (ALD). In the first step, nylon66 (polymeric organic core) nanofibers having different average fiber diameters (∼100 nm, ∼250 nm and ∼650 nm) were electrospun by using different solvent systems and polymer concentrations. In the second step, uniform and conformal layer of zinc oxide (ZnO) (inorganic shell) with precise thickness (∼90 nm) and composition on the round surface of the nylon nanofibers were deposited by ALD. The core-shell nylon66-ZnO nanofibers have shown unique properties such as structural flexibility due to the polymeric core and photocatalytic activity due to the ZnO shell layer.
Open Access
A homogeneous system for photogeneration of hydrogen initiated by bodipy based photoinduced electron transfer
(2015-08) Atılgan, Hale
The key technology to fulfill the energy needs in the future is the generation of fuels by harvesting solar energy. Due to high abundance and low prices of cobalt, water-splitting (based on cobalt) method has received a lot of attention compared to noble metals. Several times cobaltoxime based catalysts were studied for proton reduction. In this project, our aim was to produce a homogeneous photocatalytic system for photogeneration of hydrogen with high efficiency. To do so, we synthesized ten integrated molecules in which we are making use of the highly quantum efficient and photostable BODIPY chromophore. After the synthesis and characterization of target molecules, we achieved to demonstrate hydrogen evolution with five of our molecules.
Open Access
Influence of the sol – gel preparation method on the photocatalytic NO oxidation performance of TiO2/Al2O3 binary oxides
(Elsevier, 2015-03-01) Soylu, A. M.; Polat, M.; Erdogan, D. A.; Erguven, H.; Ozensoy, E.; Vovk, E. I.
In the current work, TiO2/Al2O3 binary oxide photocatalysts were synthesized via two different sol-gel protocols (P1 and P2), where various TiO2 to Al2O3 mole ratios (0.5 and 1.0) and calcination temperatures (150-1000 degrees C) were utilized in the synthesis. Structural characterization of the synthesized binary oxide photocatalysts was also performed via BET surface area analysis, X-ray diffraction (XRD) and Raman spectroscopy. The photocatalytic NO(g) oxidation performances of these binary oxides were measured under UVA irradiation in a comparative fashion to that of a Degussa P25 industrial benchmark. TiO2/Al2O3 binary oxide photocatalysts demonstrate a novel approach which is essentially a fusion of NSR (NOx storage reduction) and PCO (photocatalytic oxidation) technologies. In this approach, rather than attempting to perform complete NOx reduction, NO(g) is oxidized on a photocatalyst surface and stored in the solidstate. Current results suggest that alumina domains can be utilized as active NOx capturing sites that can significantly eliminate the release of toxic NO2(g) into the atmosphere. Using either (P1) or (P2) protocols, structurally different binary oxide systems can be synthesized enabling much superior photocatalytic total NOx removal (i.e. up to 176% higher) than Degussa P25. Furthermore, such binary oxides can also simultaneously decrease the toxic NO2(g) emission to the atmosphere by 75% with respect to that of Degussa P25. There is a complex interplay between calcination temperature, crystal structure, composition and specific surface area, which dictate the ultimate photocatalytic activity in a coordinative manner. Two structurally different photocatalysts prepared via different preparation protocols reveal comparably high photocatalytic activities implying that the active sites responsible for the photocatalytic NO(g) oxidation and storage have a non-trivial nature.
Open Access
The Janus GePas monolayer for efficient photocatalytic water splitting
(2021-08) Özbey, Doğukan Hazar
The sun is considered an inexhaustible natural energy resource compared to fos-sil fuels. Regarding the limited amount of fuels such as coal and petroleum and their eﬀect on nature, any application that has the ability to harvest the sun-light and produce energy becomes extremely important. One of the potential mechanisms that can remedy the energy demand in the future is photocatal-ysis, and two-dimensional (2D) materials with suitable electronic and optical properties oﬀer new possibilities for photocatalytic applications. Although vari-ous 2D materials have hitherto been speciﬁed as adequate candidates, materials with high photocatalytic eﬃciency for water splitting are still minimal. In this regard, a novel 2D Janus GePAs monolayer is predicted and its capability for photocatalytic water splitting is examined by performing ﬁrst-principles density functional theory. The GePAs monolayer is shown to possess robust dynamic and thermal stability. The direct electronic band gap in the visible region and band edge positions of the strain-free and strained monolayers are revealed to be convenient for redox reactions in wide pH ranges. The low recombination proba-bility of charge carriers ensured by high and anisotropic carrier mobility enhances the material’s photocatalytic potential. Optical response calculations, including many-body interactions, exhibit signiﬁcant optical absorption capacity in the UV–visible range. Furthermore, ultra-low exciton binding energy facilitates dis-sociation into free electrons and holes, promoting photocatalytic reactions. Our study suggests GePAs monolayer is an ideal and remarkably promising material to be utilized in visible-light-driven photocatalytic applications.
Open Access
Morphological control of mesoporosity and nanoparticles within Co3O4-CuO electrospun nanofibers: quantum confinement and visible light photocatalysis performance
(American Chemical Society, 2017-09) Pradhan, A. C.; Uyar, Tamer
The one-dimensional (1D) mesoporous and interconnected nanoparticles (NPs) enriched composite Co3O4-CuO nanofibers (NFs) in the ratio Co:Cu = 1/4 (Co3O4-CuO NFs) composite have been synthesized by electrospinning and calcination of mixed polymeric template. Not merely the mesoporous composite Co3O4-CuO NFs but also single mesoporous Co3O4 NFs and CuO NFs have been produced for comparison. The choice of mixed polymer templates such as polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) for electrospinning is responsible for the formation of 1D mesoporous NFs. The HR-TEM result showed evolution of interconnected nanoparticles (NPs) and creation of mesoporosity in all electrospun NFs. The quantum confinement is due to NPs within NFs and has been proved by the surface-enhanced Raman scattering (SERS) study and the UV-vis-NRI diffuse reflectance spectra (DRS). The high intense photoluminescence (PL) spectra showing blue shift of all NFs also confirmed the quantum confinement phenomena. The lowering of PL spectrum after mixing of CuO in Co3O4 nanofibers framework (Co3O4-CuO NFs) proved CuO as an efficient visible light response low cost cocatalyst/charge separator. The red shifting of the band gap in composite Co3O4-CuO NFs is due to the internal charge transfer between Co2+ to Co3+ and Cu2+, proved by UV-vis absorption spectroscopy. Creation of oxygen vacancies by mixing of CuO and Co3O4 also prevents the electron-hole recombination and enhances the photocatalytic activity in composite Co3O4-CuO NFs. The photocurrent density, Mott-Schottky (MS), and electrochemical impedance spectroscopy (EIS) studies of all NFs favor the high photocatalytic performance. The mesoporous composite Co3O4-CuO NFs exhibits high photocatalytic activity toward phenolic compounds degradation as compared to the other two NFs (Co3O4 NFs and CuO NFs). The kinetic study of phenolic compounds followed first order rate equation. The high photocatalytic activity of composite Co3O4-CuO NFs is attributed to the formation of mesoporosity and interconnected NPs within NFs framework, quantum confinement, extended light absorption property, internal charge transfer, and effective photogenerated charge separations.
Open Access
Multifunctional ZnO nanorod-reduced graphene oxide hybrids nanocomposites for effective water remediation: effective sunlight driven degradation of organic dyes and rapid heavy metal adsorption
(Elsevier, 2017-10) Ranjith, K. S.; Manivel, P.; Rajendrakumar, R. T.; Uyar, Tamer
We demonstrate the multi-functionality engineering on nanocomposite by combining one dimensional (1D) ZnO nanorod (NR) and two dimensional (2D) reduced graphene oxide (rGO) for efficient water remediation. Nano-engineered ZnO NR-rGO nanocomposites show efficient water remediation in terms of degradation of organic dyes and removal of heavy metal ions. Herein, we report on the fabrication of ZnO NR-rGO nanocomposite via a facile template-free hydrothermal route with an aim to improve the visible photocatalytic efficiency of the ZnO NR based nanocomposites. The structural and morphological features reveal that the rGO sheets are attached on the ZnO NRs and form a hybrid composite assembly. The surface enabled ZnO NR-rGO nanocomposites were used to degrade organic dye molecules (methylene blue (MB), methyl orange (MO) and rhodamine B (RhB)) under visible irradiation and adsorb Cu (II) and Co (II) ions from water through an adsorption process. The nanocomposite containing 7.5 wt% rGO and ZnO NRs shows a 4-fold enhancement in the visible photocatalytic activity and effective removal of Cu (II) and Co (II) ions from aqueous solution respectively. The photocatalytic performance is discussed in detail with respect to interaction between ZnO NRs and rGO sheets, light-harvesting properties of the nanocomposites. The effective experimental adsorption data also fit very well with the pseudo-second-order model which reveals the surface adsorption of metal ions. The results provide insight into a new method utilize for both visible photo degradation and adsorption for the removal of various wastewater pollutants. Construction of hybrid form of nanostructures delivers the effective catalytic properties with tunable functionalities for the water remediation.
Open Access
Nanocomposite synthesis of silver doped magnesium oxide incorporated in PVC matrix for photocatalytic applications
(Springer, 2021-04-08) Rouabah, N.; Boudine, B.; Nazir, Roshan; Zaabat, M.; Alqahtani, A. S.; Alqahtani, M. S.; Syed, R.
This work reveals a sol–gel approach for synthesis of silver doped magnesium oxide (Ag:MgO) incorporated in PVC matrix to give Ag:MgO/PVC nanocomposite. On glass substrate three different percentages of Ag:MgO/PVC (3,7, and 10%) were deposited by spin coating method. This film of Ag:MgO/PVC nanocomposites were characterized using AFM, UV–Vis, XRD and FTIR analysis. The results of XRD revealed the formation of Ag doped MgO nanoparticles with two phases (MgO and metallic Ag) in the matrix of PVC with the average size of nanoparticles equal to 31.5,22.29, 23.77, 29.68 nm. The direct band gap energy for PVC and pure MgO/PVC was 4.1 eV and 3.85 eV respectively. The band gap energy value changes from 3.85 eV, 3.75 eV, 3.71 eV, 3.69 eV with increasing Ag:MgO concentration(3–10%). Atomic force microscopyalso shows a change in the roughness of the nanocomposites film with increasing Ag:MgO nanoparticles percentage. The photocatalytic activity of this nanocomposite film was evaluated for the methylene blue (MB) dye under UV light irradiation. The result demonstrated good potential of Ag:MgO/PVC nanocomposites films for MB degradation with a suitable photocatalytic reaction proposed mechanism. The kinetic studies revealed a rate constant of 6.25 × 10–3 min−1 for 10% Ag:MgO/PVC nanocomposite thin films.
Open Access
Nanograined surface shell wall controlled ZnO–ZnS core–shell nanofibers and their shell wall thickness dependent visible photocatalytic properties
(Royal Society of Chemistry, 2017) Ranjith, K. S.; Senthamizhan A.; Balusamy, B.; Uyar, Tamer
The core-shell form of ZnO-ZnS based heterostructural nanofibers (NF) has received increased attention for use as a photocatalyst owing to its potential for outstanding performance under visible irradiation. One viable strategy to realize the efficient separation of photoinduced charge carriers in order to improve catalytic efficiency is to design core-shell nanostructures. But the shell wall thickness plays a vital role in effective carrier separation and lowering the recombination rate. A one dimensional (1D) form of shell wall controlled ZnO-ZnS core-shell nanofibers has been successfully prepared via electrospinning followed by a sulfidation process. The ZnS shell wall thickness can be adjusted from 5 to 50 nm with a variation in the sulfidation reaction time between 30 min and 540 min. The results indicate that the surfaces of the ZnO nanofibers were converted to a ZnS shell layer via the sulfidation process, inducing visible absorption behavior. Photoluminescence (PL) spectral analysis indicated that the introduction of a ZnS shell layer improved electron and hole separation efficiency. A strong correlation between effective charge separation and the shell wall thickness aids the catalytic behavior of the nanofiber network and improves its visible responsive nature. The comparative degradation efficiency toward methylene blue (MB) has been studied and the results showed that the ZnO-ZnS nanofibers with a shell wall thickness of ∼20 nm have 9 times higher efficiency than pristine ZnO nanofibers, which was attributed to effective charge separation and the visible response of the heterostructural nanofibers. In addition, they have been shown to have a strong effect on the degradation of Rhodamine B (Rh B) and 4-nitrophenol (4-NP), with promising reusable catalytic efficiency. The shell layer upgraded the nanofiber by acting as a protective layer, thus avoiding the photo-corrosion of ZnO during the catalytic process. A credible mechanism for the charge transfer process and a mechanism for photocatalysis supported by trapping experiments in the ZnO-ZnS heterostructural system for the degradation of an aqueous solution of MB are also explicated. Trapping experiments indicate that h+ and OH are the main active species in the ZnO-ZnS heterostructural catalyst, which do not effectively contribute in a bare ZnO catalytic system. Our work also highlights the stability and recyclability of the core-shell nanostructure photocatalyst and supports its potential for environmental applications. We thus anticipate that our results show broad potential in the photocatalysis domain for the design of a visible light functional and reusable core-shell nanostructured photocatalyst.