Ex-situ Synthesis Research Articles

Surface modification of TiO2 with copper clusters for band gap narrowing

Surface modification of photocatalytic materials to give better activity and potentially extending the response into the visible spectrum, is an area of active research. In this work, DFT modelling suggests that surface modification of rutile and anatase TiO2 with partially oxidised copper clusters can induce a red shift in the photo-action spectrum. Copper clusters were synthesised and characterised separately before TiO2 nanoparticle surface modification. Characterisation of copper clusters and photocatalysts modified with copper clusters showed that ex-situ synthesis can control the size of surface clusters. Sub-nanometre clusters of copper maintained their size and morphology upon attachment to the photocatalyst surface. The copper clusters were determined to be a mixture of Cu(0) and Cu(I), and no significant change in the oxidation state was observed following surface modification or following photoelectrochemical measurements. Experimental measurements including UV–Vis spectroscopy and valence band XPS showed a small red shift the band gap correlating to the DFT predictions. Photoelectrochemical characterisation showed an enhancement in the UV photocurrent response and a small red shift in the effective band gap for the surface modified TiO2.

Removal of antibiotics, antibiotic-resistant bacteria and their associated genes by graphene-based TiO2 composite photocatalysts under solar radiation in urban wastewaters

The present work investigated: (i) the removal of the antibiotics sulfamethoxazole (SMX), erythromycin (ERY) and clarithromycin (CLA); (ii) the inactivation of the total and antibiotic-resistant E. coli along with their regrowth potential after treatment; (iii) the removal of the total genomic DNA content; and (iv) the removal of selected antibiotic resistance genes (ARGs), namely sul1, ampC, ermB, mecA, as well as species-specific sequences, namely ecfX for Pseudomonas aeruginosa and enterococci-specific 23S rRNA, by graphene-based TiO2 composite photocatalysts under solar radiation, in real urban wastewaters. TiO2-reduced graphene oxide (TiO2-rGO) composite photocatalysts were synthesized by two ex-situ synthesis methods, namely hydrothermal (HD) treatment and photocatalytic (PH) treatment, starting from graphene oxide and Aeroxide P25 TiO2, and were characterized with various techniques, such as XRD, FT-IR, Raman, XPS, SEM and surface area (BET) analyses. The potential of the synthesized TiO2-rGO composites for the removal of the abovementioned antibiotic-related microcontaminants was compared to the efficiency shown by pristine Aeroxide P25 TiO2 under simulated solar radiation, in real urban wastewater effluents treated by a membrane bioreactor. The results showed that TiO2-rGO-PH was more efficient in the photocatalytic degradation of ERY (84±2%) and CLA (86±5%), while degradation of SMX (87±4%) was found to be slightly higher with Aeroxide P25 TiO2. It was also demonstrated that more than 180min of treatment were satisfactory for the complete inactivation and complete absence of post-treatment regrowth of E. coli bacteria (<LOD) even 24h after the end of the treatment, for all examined photocatalytic materials. The least amount of regrowth at all experimental times was observed in the presence of TiO2-rGO-HD. Moreover, the synthesized graphene-based photocatalysts successfully removed ampC and significantly reduced ecfX abundance of Pseudomonas aeruginosa, but sul1, ermB and 23S rRNA for enterococci sequences were found to be persistent throughout treatment with all catalyst types. Finally, the total DNA concentration remained stable throughout the photocatalytic treatment (4.2–4.8ngμL−1), indicating the high total genomic DNA stability in treated wastewater and its resistance to photocatalytic treatment.

Electrophoretic Deposition of Functionalized Multi-Walled Carbon Nanotubes (f-MWCNTs)-Polyaniline (PANi)

Electrophoretic deposition (EPD) is a technique that uses electric field to deposit particles onto a conductive substrate. In this study, EPD technique has been utilized for fabrication of acid functionalized multi-walled carbon nanotubes (f-MWCNTs) and polyaniline (PANi) or denoted as (f-MWCNTs-PANi) nanocomposite film. The nanocomposite was prepared using ex-situ synthesis. This study revealed that the f-MWCNTs and protonated PANi in dimethyl formamide (DMF) can be well dispersed with addition of magnesium nitrate hexahydrate, Mg (NO3)2.6H2O. The fabricated films were characterized by Fourier Transform-Infrared Spectroscopy (FT-IR) and X-Ray Photoelectron Spectroscopy (XPS). Their surface morphologies were characterized by Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscope (TEM). FT-IR results indicate the presence of carboxyl groups in f-MWCNTs spectrum. The presence of PANi was detected in the spectrum of f-MWCNTs-PANi nanocomposite. These results were further supported by FESEM and TEM results that show the morphology of f-MWCNTs and PANi coating around their sidewalls. The use of Mg (NO3)2.6H2O as dispersant for f-MWCNTs and protonated PANi allowed efficient EPD of their nanocomposite film fabrication. The fabricated f-MWCNTs-PANi composite thin film has future application in the development of supercapacitor device.

Catalysts based on large size-controlled Pd nanoparticles for aqueous-phase hydrodechlorination

This work is aimed at evaluating the catalytic performance of Pd/C catalysts based on size-controlled nanoparticles (mean size 10–50nm). Carbon black was used as support and the catalysts were tested in the aqueous phase hydrodechlorination of 4-chlorophenol. The Pd precursor was reduced with a methanol/water (10%vol.) mixture in the presence of PVP (PVP/Pd molar ratio 5–35) as capping agent. The performances of unsupported Pd–PVP colloidal nanoparticle and the catalysts prepared by impregnation of them on the carbon black (ex-situ synthesis), reduction of the precursor in the presence of that support (in-situ synthesis) and wetness impregnation were compared. The ex-situ preparation with less content of PVP (PVP/Pd molar ratio of 5) boosted the activity of the Pd–PVP nanoparticles from 16.8 to 167mmolgPd−1min−1 showing the role of the support in enhancing the catalytic performance. The in-situ synthesis with less content of PVP (PVP/Pd molar ratio of 5) resulted in catalysts with lower activity than that prepared by ex-situ synthesis, although they exhibited higher ability to hydrogenate phenol to cyclohexanone and cyclohexanol, which can be related to the morphology of the nanoparticles synthesized. Regardless of the type of synthesis, as PVP dose in synthesis increased, activity and selectivity to hydrogenation products decreased. High activity values were obtained (20–167mmolgPd−1min−1) taking into account the high mean size of the Pd nanoparticles in the catalysts.

SHS amidst other new processes for in-situ synthesis of Al-matrix composites: A review

The in-situ synthesized Al-matrix composites exhibited better mechanical properties than the composites prepared by ex-situ synthesis. Several in-situ processes for production of carbide-reinforced Al-matrix composites were comparatively discussed. The benefits of SHS process as compared to other insitu techniques are highlighted. The use of halide salts replacing elemental Ti in SHS reactions turned helpful for in-situ generation of nano particles in the Al matrix. The size, shape, and distribution of in-situ prepared reinforcing particles in Al-matrix are uniform and homogeneous. The reinforced surface is compatible with the undoped matrix surface, thus providing strong bonding. The formation of particle clusters and agglomerates can be minimized or eliminated by proper choice of in-situ processing conditions. Also addressed are the problems concerning the formation of Al3Ti and Al4C3 intermetallics as byproducts.

Capillarity-induced selective ex-situ synthesis of metal–organic framework inside mesoporous nanotubes

A general synthetic strategy to confine metal–organic frameworks (MOFs) selectively and evenly inside lumen of mesoporous nanotubes is presented. This process includes even loading of a precursor for MOF among the nanotubes in a solution phase, and following ex-situ solvothermal reaction while the precursor is suspended exclusively inside the lumen of the nanotube by capillary action, where the nanotube acts as a template as well as an ultra-small vial. The hybrid exhibits unique gas adsorption behavior, in which both microporosity and mesoporosity exist simultaneously. Confining environment of the nanotube results in a preference of the growing MOF to a specific growth direction. Enhanced water stability of inner MOF is also observed.

Conversion of 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST) from a Simple Optical Material to a Versatile Optoelectronic Material.

4-N,N-dimethylamino-4’-N’-methyl-stilbazolium tosylate (DAST) is an important optical material, but its poor conductivity limits applications in devices. To tackle this problem, we designed, prepared, and systematically investigated novel binary composite films that are composed of two-dimensional (2D) DAST and 2D graphene. Results indicate that both electrical and optical properties of DAST can be significantly improved by graphene addition. The negative steric effects of big DAST molecules that greatly trouble ex-situ synthesis can be efficiently overcome by in-situ synthesis, thus leading to better film quality and higher physical properties. Consequently, the in-situ composite film exhibits a low sheet resistance of 7.5 × 106 ohm and high temperature coefficient of resistance of −2.79% K−1, close to the levels of the most important bolometric materials for uncooled infrared detectors. Particularly, a new low temperature reduction of graphene oxide induced by DAST, which is further enhanced by in-situ process, was discovered. This work presents valuable information about the DAST–graphene composite films, their chemical structures, mechanisms, physical properties, and comparison on in-situ and ex-situ syntheses of graphene–based composites, all of which will be helpful for not only theoretically studying the DAST and graphene materials and expanding their applications, but also for seeking new optoelectronic sensitive materials.

Synthesis of catalytically active rock salt structured MgxNb1−xO nanoparticles for MgH2 system

This communication deals with the ex-situ synthesis of rock salt type MgxNb1−xO whose structural characteristics are closely related with MgO. XRD examination of 30 h ball milled MgH2 + Nb2O5 confirms the formation of a rock salt product MgxNb1−xO, which is comparable to the recently reported active catalyst MgxNb1−xO formed in-situ in MgH2 milled with 8 mol.% Nb2O5. It is shown that MgH2 catalyzed with the pre-made 2 wt.% MgxNb1−xO desorbs hydrogen at least 50 °C lower than the in-situ 2 wt.% Nb2O5 catalyzed MgH2 with improved reversible absorption. This result highlights that the proposed pathway mechanism on the basis of Nb2O5 catalyst may need further verification and that the addition of the MgxNb1−xO catalyst in a pre-reduced state can offer distinct performance advantages over its in-situ preparation.