Photodeposition Process Research Articles

Plasmonic Au-NPs photodecorated on NiCoLDH nanosheets as a flexible SERS sensor for the real-time detection of fipronil

Rapid extraction and detection of probe molecules from curved surfaces is critical for on-site and real-time detection. In this study, a flexible platform was developed using carbon cloth (CC) to create honeycomb-like nickel cobalt layered double hydroxides (NiCoLDH) nanosheets via a simple electrodeposition technique, which were then decorated with gold nanoparticles (Au-NPs) via photodeposition process. The Au-NPs/NiCoLDH/CC was designed as a surface-enhanced Raman scattering (SERS) substrate for detecting the broad-spectrum insecticide, Fipronil (FP). The fabricated sensor achieves a superior SERS activity due to the electrodeposited NiCoLDH, which provides the charge-transfer effect, and the photodeposited Au-NPs, which generate efficient SERS hotspots through the electromagnetic effect. The Density Functional Theory (DFT) calculation was used to estimate the optimal geometry and frontier molecular orbital diagrams of the FP molecules. The influence of electrodeposition time on NiCoLDH production and Au-NPs decorating quantity was investigated in detail. Furthermore, the flexible SERS sensor has excellent sensitivity, homogeneity, a low limit of detection (LOD), and high reproducibility for FP detection. Even after 40 cycles of bending and torsion, the SERS substrate maintained excellent mechanical endurance. Through a direct-sampling approach, FP molecules on the surfaces and mesocarp region of grapes and tomatoes were successfully detected with lower LOD. These findings highlight the outstanding potential of the produced flexible SERS sensor for real-time and on-site insecticide detection, making it valuable for food security analysis and monitoring.

Insight of indium single atom loading on TiO2 for remarkable photocatalytic hydrogen evolution

Hydrogen production by photocatalysis water splitting is an attractive and promising development method, but the current efficiency is too low for application. Loading single atoms can significantly enhance the photocatalytic efficiency, however, the insightful understanding of the impact of single atom loading on catalytic performance is still ambiguous. In this work, InSA/TiO2 photocatalysts modified with indium single atom (InSA) were synthesized by photo-deposition process. Under 300W Xe lamp illumination, the hydrogen production rate of the optimized InSA/TiO2 photocatalyst achieves 6.11 mmol g−1 h−1, which is 7.6 times that of TiO2 prepared under the same conditions. The results of characterization analysis and density functional theory (DFT) calculations indicate that some of the Ti atoms on the TiO2 surface are replaced by the doped In, and the local electronic structures of the photocatalyst are regulated, which results in effectively separating of the photo-generated carriers, and significant increasing the activity of the surrounding unsaturated oxygen, thus, the photocatalytic hydrogen production performance is effectively improved. This work provides a strategy to improve photocatalytic activity, and also deepens the understanding of metal single atom modification mechanism.

In situ photodeposition of ultra-small palladium particles on TiO2.

In situ and operando investigation of photocatalysts plays a fundamental role inunderstanding the processes of active phase formation and the mechanisms ofcatalytic reactions, which is crucial for the rational design of more efficient materials. Using a custom-made operando photocatalytic cell, an in situ procedure to follow the formation steps of Pd/TiO2 photocatalyst by synchrotron-based X-ray absorption spectroscopy (XAS) is proposed. The procedure resulted in the formation of ∼1 nm Pd particles with a much narrower size distribution and homogeneous spreading over TiO2 support compared with the samples generated in a conventional batch reactor. The combination of in situ XAS spectroscopy with high-angle annular dark-field scanning transmission electron microscopy demonstrated the formation of single-atom Pd(0) sites on TiO2 as the initial step of the photodeposition process. Palladium hydride particles were observed for all investigated samples upon exposure to formic acid solutions.

Enhanced light harvesting ability in hollow Pt/TiO2 nanoreactor for boosting tetracycline photodegradation

Utilizing solar energy to decompose tetracycline (TC) is a green strategy to treat wastewater. Herein, a heterogeneous hollow structured TiO2 decorated Pt nanoparticles were successfully designed and synthesized via hard-template approach and photo-deposition process toward TC photodegradation. The Pt nanoparticles loaded on the surface of hollow structured TiO2 can increase the visible light absorption due to the local surface plasmon resonance (LSPR) effect. Furthermore, owing to the tough electron oscillation of the LSPR excitation, the plasmonic hot holes on the surface of Pt nanoparticles can capture the electrons of TiO2, effectively facilitating the separation of photo-excited charge carriers because of the formation of Schottky junction constructed between Pt and TiO2. Combined the natural merits of shorten conveying path of charge carriers and physical structural stability for hollow structure, the optimal Pt/TiO2 hetero-junction hybrid showed superior photocatalytic activity and durability for TC photodegradation with the degradation efficiency of 93.8 ​% after 30 ​min and the rate constant of 0.09196 min−1 under 300 ​W Xe lamp irradiation. This work displays a heterogeneous hybrids catalyst based on eco-friendly metal and semiconductor materials which can be used in the fields including without limitation TC photodegradation.

Comprehensive spectroscopy and photocatalytic activity analysis of TiO2-Pt systems under LED irradiation

This study presents a thorough spectroscopic analysis of TiO2-Pt systems under LED irradiation, with a focus on elucidating the photodeposition process of Pt nanoparticles onto TiO2 surfaces. The methodology leverages an innovative LED photoreactor tailored to a specific spectral range, enabling precise characterization of the excitation spectrum of TiO2-Pt composites. Through the identification of Pt precursor species and their excitation under LED-UV light, a photodeposition mechanism is proposed involving concurrent excitation of both the TiO2 semiconductor and the H2PtCl6 precursor. The LED photoreactors are employed to scrutinize the excitation profile of TiO2-Pt materials, revealing that the incorporation of Pt nanoparticles does not expand TiO2's absorption spectrum. Furthermore, UV-A exposure in the absence of Pt did not induce the formation of surface defects, underscoring the lack of visible light activity in TiO2-Pt systems. Spectroscopic analyses, complemented by naproxen photooxidation experiments, indicate the absence of a significant plasmonic effect in Pt nanoparticles within the experimental framework. Mass spectroscopy results corroborate the presence of distinct naproxen degradation pathways, suggesting minimal influence from photocatalyst properties. This research provides a detailed spectroscopic insight into TiO2-Pt photocatalysis, enriching the knowledge of photocatalytic materials in LED lighting.

Photodeposition-Based Synthesis of TiO2@IrOx Core-Shell Catalyst for Proton Exchange Membrane Water Electrolysis with Low Iridium Loading.

The widespread application of green hydrogen production technologies requires cost reduction of crucial elements. To achieve this, a viable pathway to reduce the iridium loading in proton exchange membrane water electrolysis (PEMWE) is explored. Herein, a scalable synthesis method based on a photodeposition process for a TiO2@IrOx core-shell catalyst with a reduced iridium content as low as 40wt.% is presented. Using this synthesis method, titania support particles homogeneously coated with a thin iridium oxide shell of only 2.1±0.4nm are obtained. The catalyst exhibits not only high ex situ activity, but also decent stability compared to commercially available catalysts. Furthermore, the unique core-shell structure provides a threefold increased electrical powder conductivity compared to structures without the shell. In addition, the low iridium content facilitates the fabrication of sufficiently thick catalyst layers at decreased iridium loadings mitigating the impact of crack formation in the catalyst layer during PEMWE operation. It is demonstrated that the novel TiO2@IrOx core-shell catalyst clearly outperforms the commercial reference in single-cell tests with an iridium loading below 0.3mgIrcm-2 exhibiting a superior iridium-specific power density of 17.9kW gIr -1 compared to 10.4kW gIr -1 for the commercial reference.

Led-induced deposition of Pt and Au NPs on carbon fibers: Developing a novel strategy for facile fabrication of electrocatalysts for enhanced methanol electrooxidation

In addressing the imperative of aligning materials science with sustainable development, our study introduces an innovative method for the simultaneous deposition of Pt and Au nanoparticles onto a carbon support. This research represents the pioneering application of the photodeposition process for synthesizing bimetallic nanoparticles on a carbon matrix. The comprehensive characterization of the resulting nanostructures involves various techniques, including field X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), atomic force microscopy (AFM), energy-dispersive X-ray analysis (EDX), inductively coupled plasma atomic emission spectroscopy (ICP-OES), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetric techniques. Our findings reveal that the photodeposition method produces a homogeneous AuPt nanostructure, demonstrating superior electrocatalytic activity in methanol oxidation compared to the monometallic carbon fiber_Pt (CF_Pt) catalyst. These results emphasize the effectiveness of our novel approach in fabricating electrocatalysts with exceptional performance in methanol oxidation reactions.

IrO2 Oxygen Evolution Catalysts Prepared by an Optimized Photodeposition Process on TiO2 Substrates.

Preparing high-performance oxygen evolution reaction (OER) catalysts with low precious metal loadings for water electrolysis applications (e.g., for green hydrogen production) is challenging and requires electrically conductive, high-surface-area, and stable support materials. Combining the properties of stable TiO2 with those of active iridium oxide, we synthesized highly active electrodes for OER in acidic media. TiO2 powders (both commercially available Degussa P-25® and hydrothermally prepared in the laboratory from TiOSO4, either as received/prepared or following ammonolysis to be converted to titania black), were decorated with IrO2 by UV photodeposition from Ir(III) aqueous solutions of varied methanol scavenger concentrations. TEM, EDS, FESEM, XPS, and XRD measurements demonstrate that the optimized version of the photodeposition preparation method (i.e., with no added methanol) leads to direct deposition of well-dispersed IrO2 nanoparticles. The electroactive surface area and electrocatalytic performance towards OER of these catalysts have been evaluated by cyclic voltammetry (CV), Linear Sweep Voltammetry (LSV), and Electrochemical Impedance Spectroscopy (EIS) in 0.1 M HClO4 solutions. All TiO2-based catalysts exhibited better mass-specific (as well as intrinsic) OER activity than commercial unsupported IrO2, with the best of them (IrO2 on Degussa P-25® ΤiO2 and laboratory-made TiO2 black) showing 100 mAmgIr-1 at an overpotential of η = 243 mV. Chronoamperometry (CA) experiments also proved good medium-term stability of the optimum IrO2/TiO2 electrodes during OER.

0D/1D CuO-Cu2O/ZnO p-n heterojunction with high photocatalytic activity for the degradation of dyes and Naproxen

The development of highly active photocatalysts with broad spectrum response is of paramount importance for photocatalytic applications. Herein, heterostructured CuO-Cu2O/ZnO photocatalysts were prepared in a single step and under mild conditions using a photodeposition process which allows to deposit CuO-Cu2O particles with an average size of ca. 2.4 nm on the surface of ZnO nanorods. The p-n heterojunction built between CuO-Cu2O and ZnO allows to increase both the visible light response of the photocatalyst and the charge separation. The CuO-Cu2O(10%)/ZnO catalyst exhibits the highest activity for the degradation of dyes (Rhodamine B and Remazol Brilliant Blue R) and of Naproxen under simulated solar light irradiation. Based on scavenging experiments, holes, superoxide radicals O2●- and singlet oxygen 1O2 are the dominant species involved in the photocatalytic degradation and a mechanism is proposed. Due to its high stability and photocatalytic performance in various water matrices, the CuO-Cu2O(10%)/ZnO nanohybrid is of high potential for the large scale remediation of organic pollutants in wastewater.

Implementing a sustainable process for the recovery of palladium from spent catalysts at industrial scale: A LCA approach

Due to its unique physicochemical properties, palladium is widely used in several industry applications (e.g., vehicle emission control). In view of the circular economy, it is essential to explore secondary sources of palladium, such as urban mines. Current technologies for effective palladium recovery involve high energy consumption and severe environmental impact. More recently, a novel green method for recovering palladium from spent catalysts through a combination of mild acidic leaching and photodeposition on ZnO nanoparticles was proposed on a laboratory scale. In the present study, the environmental impacts of this recovery method, properly upscaled and modelled, was assessed by employing the LCA approach. Specifically, a comparative LCA was carried out for the process with as well as without recycling key components, such as Cu (II) and NaCl for the leaching solution and ZnO. The outcomes identified critical areas and drove the investigation of alternative process configurations to reduce its environmental footprint, such as the use of carbon dioxide in the photodeposition process with the aim of decreasing the resulting terrestrial ecotoxicity. This study marks a significant step forward in advancing research toward industrial−scale implementation of palladium recovery. It provides valuable insights for researchers in the field of green physicochemical processes for metal recovery, thus offering guidance for future decision−making towards more sustainable practices.

Electrochemical investigations and antimicrobial activity of Au nanoparticles photodeposited on titania nanoparticles

Titanium oxide nanopowder (TiO2 NPs) was synthesized via anodization in 0.7 M perchloric acid then annealed in nitrogen at 450 °C for 3 h to prepared the Titanium Oxide Nitrogen annealed nanoparticles (TiO2 NPs-N2) powder as catalytic support. Using a photodeposition process, gold was added with isopropanol as a sacrificial donor and H[AuCl4] acid, producing gold nanoparticles on nitrogen-annealed titanium oxide nanoparticles (Au-NPs on TiO2-NPs-N2). The mass loading of Au NPs was 2.86 × 10−4 (g/cm2). TEM images of Au NPs on TiO2-NPs-N2 suggest circular particles with a tendency to agglomerate. Cyclic voltammetry (CV) was used to investigate the electrocatalytic performance of the Au NPs/TiO2-NPs-N2 catalysts in ferrocyanide, KOH, and H2SO4, and the results were compared to those of a polycrystalline Au electrode that is readily accessible in the market. In KOH, H2SO4, and (2 M KOH + 0.1 M glycerol) solutions, the Au NPs/TiO2-NPs-N2 electrode displayed a startlingly high electrocatalytic performance. Using CV, the electrocatalytic oxygen reduction reaction (ORR) of Au NPs/TiO2-NPs-N2 and Au-NPs against glycerol oxidation in basic media was studied. The results indicated that Au NPs/TiO2-NPs-N2 is a promising support material for improving the electrocatalytic activity for acidic and basic oxidation. The electrode made of Au NPs/TiO2-NTs-N2 has steady electrocatalytic activity and may be reused repeatedly. TiO2 NPs and Au NPs/TiO2NPs-N2 showed satisfactory antibacterial activity against some human pathogenic bacteria using the disc diffusion method.

Efficient photocatalytic reduction of p-nitrophenol under visible light irradiation based on Ag NPs loaded brown 2D g-C3N4 / g-C3N4 QDs nanocomposite

Recently, low-cost graphitic carbon nitride (g-C3N4) revealed high photocatalytic activities and provided solutions to environmental pollution. In this study, we synthesized brown mesoporous 2D g-C3N4 by calcination dicyandiamide with pluronic P123. This is followed by loading of Ag NPs on the prepared 2D g-C3N4 by photodeposition process. After that, a ternary composite 2% Ag/ 2D g-C3N4 / g-C3N4 QDs heterojunction photocatalyst has been successfully prepared. The prepared nanomaterials were comprehensively characterized by various analysis techniques such as XRD, UV–Vis., BET, XPS, SEM, TEM. This new system exhibited a large surface area with porous structure and a wide absorption of visible light. The results verified that Ag NPs decoration enhanced the charge separation of photo-generated carriers of g-C3N4 2D and g-C3N4 QDs, promote significant enhancement in the photocatalytic activity for reduction of p-nitrophenol with a rate constant (k) value of 0.49729 / min in 6 min. This rate is about two-fold higher than that observed for pure g-C3N4 2D and g-C3N4 QDs as well as shows an improvement compared to 2% Ag/ g-C3N4 2D and g-C3N4 2D/ g-C3N4 QDs. The results open the door to design highly efficient 2D/0D nanocomposite photocatalysts for a wide variety of environmental applications.

In-situ synthesized oxygen vacancy filled ZnS/Vo-ZnO heterojunction photocatalysts for efficient H2 production

Defect-filled ZnO-based heterojunctions have gained attention in photocatalytic hydrogen (H2) production due to their ability to reduce the recombination rate of photogenerated carriers at the heterojunction interface. In this study, the surface oxygen vacancy defects on ZnO (Vo-ZnO) were precisely tailored by decomposing the deep eutectic solvents (DES) prepared ZnO/Zn(OH)2 complex. The defective surfaces of Vo-ZnO act as nucleation sites for binding S atoms on their oxygen vacancies during in-situ photodeposition, resulting in the formation of ZnS. In this process, oxygen vacancies on the surface are electronically filled, and ZnS is simultaneously grown on ZnO. As a result, the ZnS/Vo-ZnO heterojunction photocatalyst exhibits a higher donor charge density (ND) of 3.80 × 1021 cm−3 and reduces the charge transfer resistance (Rct) by 22 kΩ compared to Vo-ZnO. The ZnS/Vo-ZnO has an H2 production rate of 18.84 mmol g−1 h−1 and follows the type-II heterojunction for charge separation. The prolonged photoluminescence lifetime (τave = 1.6 ns) in the ZnS/Vo-ZnO is attributed to the heterojunction interface between ZnS and defective ZnO. The proposed approach creates a new synthesis route for constructing the type-II heterojunction between ZnS and Vo-ZnO via an in-situ photodeposition process.

Defects Healing of the ZnO Surface by Filling with Au Atom Catalysts for Efficient Photocatalytic H2 Production.

Healed defects on photocatalysts surface and their interaction with plasmonic nanoparticles (NPs) have attracted attention in H2 production process. In this study, surface oxygen vacancy (Vo ) defects are created on ZnO (Vo -ZnO) NPs by directly pyrolyzing zeolitic imidazolate framework. The surface defects on Vo -ZnO provide active sites for the diffusion of single Au atoms and as nucleation sites for the formation of Au NPs by the in situ photodeposition process. The electronically healed surface defects by single Au atoms help in the formation of a heterojunction between the ZnO and plasmonic Au NPs. The formed Au/Vo -Au:ZnO-4 heterojunction prolongs photoelectron lifetimes and increases donor charge density. Therefore, the optimized photocatalysts of Au/Vo -Au:ZnO-4 has 21.28 times higher H2 production rate than the pristine Vo -ZnO under UV-visible light in 0.35m Na2 SO4 and 0.25m Na2 SO3 . However in 0.35m Na2 S and 0.25m Na2 SO3 , the H2 production rate is 25.84 mmole h-1 g-1 . Furthermore, Au/Vo -Au:ZnO-4 shows visible light activity by generating hot carries via induced surface plasmonic effects. It has 48.58 times higher H2 production rate than pristine Vo -ZnO. Therefore, this study infers new insight for defect healing mediated preparation of Au/Vo -Au:ZnO heterojunction for efficient photocatalytic H2 production.

Insight into the LED-induced deposition of Pt nanoparticles on a graphite matrix: Unravelling the photodeposition processes on materials different than semiconductors

A novel LED-assisted photodeposition process was used for the photoreduction of platinum nanoparticles on the exfoliated graphite surfaces. The photodeposition process on graphite was presented for the first time. It was found that the exfoliated graphite/Pt is graphite flakes with platinum nanocrystalline being homogeneously deposited on the surface of the carbon matrix. The mechanism of Pt photodeposition was based on the initial adsorption of Pt(IV) ions on the surface of the expanded graphite, and the reduction of Pt under the influence of UV radiation. Electrochemical measurements demonstrated that the EG/Pt composite exhibited good catalytic activity in the reaction of methanol electro-oxidation. The tested electrode maintained a high activity despite poisoning the Pt catalyst with intermediate products of methanol oxidation. This confirms that the LED-assisted photodeposition process can be an element of a novel approach for the synthesis of graphite-based materials for direct methanol fuel cells.

Insight into the LED-assisted deposition of platinum nanoparticles on the titania surface: understanding the effect of LEDs

This paper proposes a novel LED-assisted deposition of platinum nanoparticles on the titania surface. For the first time, this process was supported by a UV-LED solution. We used two light sources with different wavelengths (λmax = 365 and 395 nm), and power (P = 1, 5, and 10 W) because the photodeposition process based on LEDs has not been defined. The TiO2–Pt material was discovered to be nano-crystalline anatase particles with nano-platinum particles deposited on the surface of titanium dioxide. Furthermore, the luminescence intensity decreased when Pt was added to TiO2, indicating that charge carrier recombination was reduced. The spectra matching of the photocatalyst and LED reactor was performed for the first time in this work. We proposed a convenient LED reactor that focused light in the range of 350–450 nm, allowing us to effectively use photo-oxidative properties of TiO2–Pt materials in the process of removing 4-chlorophenol. In the presented work, the LED light source plays a dual role. They first induce the platinum photodeposition process, before becoming an important component of tailored photoreactors, which is an important innovative aspect of this research.

ALD-Deposited NiO Approaches the Performance of Platinum as a Hydrogen Evolution Cocatalyst on Carbon Nitride

The photocatalytic hydrogen evolution reaction is one of the most promising approaches to utilize solar energy and produce hydrogen as an alternative energy source to traditional fossil fuels. In this work, we focused on further exploring the cocatalyst potential of the transition metal nickel and prepared nickel oxide/carbon nitride (NiO/CNx) heterojunctions through thermal polymerization as well as plasma-enhanced atomic layer deposition (PEALD). The optimal NiO loading thickness on the surface of the CNx was found to be 6.5 nm, prepared from 65 cycles of ALD. This NiO(65)/CNx had a photocatalytic hydrogen evolution rate of 3.9 μmol h–1 in a 2 mg mL–1 aqueous photocatalyst solution (195 μmol h–1 g–1), corresponding to an AQY of 3.1% and exhibiting 54% of the activity of 3 wt % Pt/CNx under 405 nm light illumination with a sacrificial reagent. A 3 wt % Ni/CNx prepared through a photodeposition process from a dispersion of CNx and simple NiCl2 had a photocatalytic hydrogen evolution rate of 2.8 μmol h–1 (140 μmol h g–1) and an AQY of 2.2% with 2 mg mL–1 photocatalyst in the reactant solution, corresponding to 39% of the activity of 3 wt % Pt/CNx. An induction period at the beginning of the hydrogen evolution process was found in all Ni-based photocatalysts, which we related to a Ni in situ photoreduction from NiII to Ni0 and the reverse reaction. In addition, the reproducibility of the induction period even in an oxygen-free environment suggests that electrons flow back from reduced Ni species to CNx under dark conditions. Furthermore, a large population of trap states was detected in the bulk CNx materials via photoinduced absorption spectroscopy, and the trapping severely hinders cocatalysts (even the benchmark Pt cocatalyst) from extracting charges from CNx for subsequent interfacial redox reactions. We conclude that not only does the surface/interface engineering of the photocatalyst/catalyst heterojunctions need to be considered but also trap states in CNx that severely limit the transfer of photogenerated charges to cocatalysts.

Synergy of Ultrathin CoOx Overlayer and Nickel Single Atoms on Hematite Nanorods for Efficient Photo-Electrochemical Water Splitting.

To solve surface carrier recombination and sluggish water oxidation kinetics of hematite (α-Fe2 O3 ) photoanodes, herein, an attractive surface modification strategy is developed to successively deposit ultrathin CoOx overlayer and Ni single atoms on titanium (Ti)-doped α-Fe2 O3 (Ti:Fe2 O3 ) nanorods through a two-step atomic layer deposition (ALD) and photodeposition process. The collaborative decoration of ultrathin CoOx overlayer and Ni single atoms can trigger a big boost in photo-electrochemical (PEC) performance for water splitting over the obtained Ti:Fe2 O3 /CoOx /Ni photoanode, with the photocurrent density reaching 1.05mA cm-2 at 1.23V vs. reversible hydrogen electrode (RHE), more than three times that of Ti:Fe2 O3 (0.326 mA cm-2 ). Electrochemical and electronic investigations reveal that the surface passivation effect of ultrathin CoOx overlayer can reduce surface carrier recombination, while the catalysis effect of Ni single atoms can accelerate water oxidation kinetics. Moreover, theoretical calculations evidence that the synergy of ultrathin CoOx overlayer and Ni single atoms can lower the adsorption free energy of OH* intermediates and relieve the potential-determining step (PDS) for oxygen evolution reaction (OER). This work provides an exemplary modification through rational engineering of surface electrochemical and electronic properties for the improved PEC performances, which can be applied in other metal oxide semiconductors as well.

The Role of Nitrogen-Doped TiO2 Supported by Platinum Catalyst Synthesized via Various Mode Preparations for Photocatalytic Enhancement.

The limitations of TiO2 as a photocatalyst such as the larger bandgap energy, which only activates under the UV region, give a lower photocatalytic activity. This study reports the role of the N and Pt co-dopant on the modification of the TiO2 photocatalyst for photocatalytic degradation of methylene blue dye under different mode preparations, i.e., sequential and vice-versa modes. The sequential mode preparation of the N and Pt co-dopant TiO2 photocatalyst consisted of the initial preparation of the N-doped TiO2 (N-TiO2) under the calcination method, which was then further doped with platinum (Pt) through the photodeposition process labeled as NPseq-TiO2, while the vice-versa mode was labeled as PNrev-TiO2. About 1.58 wt.% of N element was found in the NPseq-TiO2 photocatalyst, while there was no presence of N element detected in PNrev-TiO2, confirmed through an elemental analyzer (CHNS-O) and (EDX) analysis. The optimum weight percentage of Pt for both modes was detected at about ±2.0 wt.%, which was confirmed by inductively coupled plasma-emission spectroscopy (ICP-OES). The photoactivity under methylene blue (MB) dye degradation of the NPseq-TiO2 photocatalyst was 2 and 1.5 times faster compared to the unmodified TiO2 and PNrev-TiO2, where the photodegradation rates were, ca., 0.065 min-1 and 0.078 min-1, respectively. This was due to the N elements being incorporated with the TiO2 lattice, which was proven by UV-Vis/DRS where the bandgap energy of NPseq-TiO2 was reduced from 3.2 eV to 2.9 eV. In addition, the N generated a stronger PL signal due to the formation of oxygen vacancies defects on the surface of the NPseq-TiO2 photocatalyst. The higher specific surface area as well as higher pore volume for the NPseq-TiO2 photocatalyst enhanced its photocatalytic activity. Moreover, the NPseq-TiO2 showed the lowest COD value, and it was completely mineralized after 7 h of light irradiation. The preparation order did not affect the Pt dopant but did for the N element. Therefore, it is significant to investigate different mode preparations of the N and Pt co-dopant for the modification of TiO2 to produce a good-quality photocatalyst for photocatalytic study under the photodegradation of MB dye.

Surface-Confined Photodeposition of Noble Metal Nanoclusters on TiO2 in a Fluidized Bed for the Catalytic Oxidation of Formaldehyde

Noble metal nanoclusters/oxides have been attracting close attention in heterogeneous catalysis due to their unique physical and chemical properties. However, due to the effect of the Schottky heterojunction, the deposited particles are easy to aggregate, and the size is difficult to control. In this work, we report a surface-confined photodeposition process to load ultrafine noble nanoclusters on semiconductor oxides, e.g., titanium oxide (TiO2), in a fluidized bed (F method). Different from the traditional photodeposition in solution (L method), the metal precursors which are absorbed on the semiconductor are difficult to migrate via the F method, therefore effectively inhibiting the agglomeration of nanoparticles. Noble metal nanoclusters with a uniform size smaller than 2 nm are obtained. In the model reaction of the catalytic oxidation of formaldehyde (HCHO), Pt/TiO2 with an ultralow loading amount (0.08 wt% Pt) showed excellent performance for the catalytic oxidation of HCHO at room temperature, which is benefited from the small and uniform size of nanoclusters. This work brings an effective strategy in the fabrication of size-controlled noble metals on oxide supports for heterogeneous catalysis.