ABSTRACT
Graphitic carbon nitride supported silver nanoparticles (AgNPs/g-C3N4) with 1%, 3%, and 5% AgNPs were successfully synthesized by an "ex situ" method with ultrasound of a mixture of AgNP solution and g-C3N4. The AgNP solution was prepared by chemical reduction with trisodium citrate, and g-C3N4 was synthesized from the urea precursor. The supported nanoparticles were characterized by X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption (BET), Fourier transformation infrared (FTIR) and Raman spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), photoluminescence spectroscopy (PL), electron paramagnetic resonance (EPR) and electrochemical impedance spectroscopy (EIS) Nyquist plots. The visible light-driven photocurrent measurement was performed by three on-off cycles of intermittent irradiation. The analyses show that AgNPs were evenly dispersed on g-C3N4, and have sizes ranging from 40 to 50 nm. The optical properties of the AgNPs/g-C3N4 material were significantly enhanced due to the plasmonic effect of AgNPs. The photocatalytic activity of catalysts was evaluated by 2,4-D degradation under visible light irradiation (λ > 420 nm). In the reaction conditions: pH 2.2; C o (2,4-D) 40 ppm; a m/v ratio of 0.5 g L-1, AgNPs/g-C3N4 materials exhibit superior photocatalytic activity compared to the pristine g-C3N4. The studies on the influence of free radicals and photogenerated holes, h+, show that ËOH, O2Ë-, and h+ play decisive roles in the photocatalytic activity of AgNPs/g-C3N4. The TOC result indicates the minimal toxicity of the by-products formed during the 2,4-D degradation. In addition, the AgNPs/g-C3N4 catalytic activity under direct sunlight irradiation was similar to that under artificial UV irradiation. Based on these results, a possible mechanism is proposed to explain the enhanced photocatalytic activity and stability of AgNPs/g-C3N4. Theoretical calculations on the interaction between 2,4-D and g-C3N4, Ag/g-C3N4 was also performed. The calculated results show that the adsorption of 2,4-D on Ag-modified g-C3N4 is significantly more effective compared to pristine g-C3N4.
ABSTRACT
The adsorption and degradation capacities of dichlorodiphenyltrichloroethane (DDT) on a photocatalyst composed of TiO2 supported on the mesoporous material MCM-41 (TiO2/MCM-41) were investigated using density functional theory and real-time density functional theory methods. The van der Waals interactions within the PBE functional were adjusted by using the Grimme approach. The adsorption of DDT was evaluated through analyses involving adsorption energy, Hirshfeld atomic charges, Wiberg bond orders, molecular electrostatic potential, noncovalent interaction analysis, and bond path analysis. The findings reveal that DDT undergoes physical adsorption on pristine MCM-41 or MCM-41 modified with Al or Fe due to the very small bond order (only about 0.15-0.18) as well as the change in total charge of DDT after adsorption is close to 0. However, it chemically adsorbs onto the TiO2/MCM-41 composite through the formation of Ti···Cl coordination bonds because the maximum bond order is very large, about 1.0 (it can be considered as a single bond). The adsorption process is significantly influenced by van der Waals interactions (accounting for approximately 30-40% of the interaction energy), hydrogen bonding, and halogen bonding. MCM-41 is demonstrated to concurrently function as a support for the TiO2 photocatalyst, creating a synergistic effect that enhances the photocatalytic activity of TiO2. Based on the computational results, a novel photocatalytic mechanism for the degradation of DDT on the TiO2/MCM-41 catalyst system was proposed.
ABSTRACT
A combination of Artificial Bee Colony algorithm, eXtended Tight Binding and Density functional theory methods were performed to study the activation process of carbon dioxide (CO2) over copper (Cu4 cluster) based catalytic systems. The findings revealed that the activation of the C-O bond resulted from the electron transfer to σ*, π* - MO of CO2. The more the electrons are transferred to CO2, the more the C-O bond is activated and elongated. The suitability of several metal oxide supports (Fe2O3, Al2O3, MgO, ZnO) is estimated using calculated electronic parameters (global electrophilicity index, vertical ionization potential and vertical electron affinity). Aside from demonstrating the appropriateness of Al2O3 and ZnO, a thorough examination of MgO revealed that, due to the formation of stable carbonate products, this oxide is not really appropriate as a support for copper-based catalysts in CO2 conversion. Our studies have also shown that the electron enrichment of copper atoms plays a key role in the activation of C-O bonds. Alkali metal doping (Li, K, Cs) significantly improves the catalytic efficiency of the Cu4 cluster. Based on the results of electron transfer to the CO2 molecule, the effect of doping alkali metal atoms may be organized in the following order: Cs > K > Li. A new core/shell catalytic system with potassium atoms in the core and copper atoms in the shell has been proposed and has proven to be a promising, efficient catalytic system in the CO2 adsorption and activation.
Subject(s)
Carbon Dioxide , Copper , Catalysis , Electrons , Models, TheoreticalABSTRACT
The density functional theory method was performed to study the electronic structures of planar (pGN), corrugated (cGN) graphitic carbon nitride and their interactions with titanium dioxide cluster (TiO2)7. The transfer of photoinduced electrons was analyzed and electronic excitations were calculated. The obtained results show that cGN is thermodynamically more stable than pGN. cGN chemically interacts with titanium dioxide clusters, while the interaction between pGN and the cluster is assigned to physical nature. The combination of cGN and pGN with (TiO2)7 reduces the energy of the first excited states compared to that of the pure substances. The photocatalytic activities were estimated based on hypotheses on the location of the reduction and oxidation sites, the distance between the photoinduced holes and electrons and the electron density of molecular orbitals involved in the excitation. cGN/TiO2 is predicted to have a higher photocatalytic activity than pGN/TiO2.
ABSTRACT
The prevalence of global arsenic groundwater contamination has driven widespread research on developing effective treatment systems including adsorption using various sorbents. The uptake of arsenic-based contaminants onto established sorbents such as activated carbon (AC) can be effectively enhanced via immobilization/impregnation of iron-based elements on the porous AC surface. Recent suggestions that AC pores structurally consist of an eclectic mix of curved fullerene-like sheets may affect the arsenic adsorption dynamics within the AC pores and is further complicated by the presence of nano-sized iron-based elements. We have therefore, attempted to shed light on the adsorptive interactions of arsenate-iron nanoparticles with curved fullerene-like sheets by using hybridized quantum mechanics/molecular mechanics (QMMM) calculations and microscopy characterization. It is found that, subsequent to optimization, chemisorption between HAsO42- and the AC carbon sheet (endothermic process) is virtually non-existent - this observation is supported by experimental results. Conversely, the incorporation of iron nanoparticles (FeNPs) into the AC carbon sheet greatly facilitates chemisorption of HAsO42-. Our calculation implies that iron carbide is formed at the junction between the iron and the AC interface and this tightly chemosorbed layer prevents detachment of the FeNPs on the AC surface. Other aspects including electronic structure/properties, carbon arrangement defects and rate of adsorptive interaction, which are determined using the Climbing-Image NEB method, are also discussed.
ABSTRACT
The activation of carbon dioxide (CO2) by catalytic systems comprising a transition metal (Co, Cu,Ni) on an activated carbon (AC) support was investigated using a combination of different theoretical calculation methods: Monte Carlo simulation, DFT and DFT-D, molecular dynamics (MD), and a climbing image nudged elastic band (CI-NEB) method. The results obtained indicate that CO2 is easily adsorbed by AC or MAC (M: Cu, Co, Ni). The results also showed that the process of adsorbing CO2 does not involve a transition state, and that NiAC and CoAC are the most effective of the MAC catalysts at adsorbing CO2. Adsorption on NiAC led to the strongest activation of the C-O bond, while adsorption on CuAC led to the weakest activation. Graphical Abstract Models of CO2 activation on: a)- activated carbon; b)- metal supported activated carbon (M-AC), where M: Co, Cu, Ni.
ABSTRACT
Density functional theory (DFT) calculations performed at the PBE/DZP level using the DFT-D2 method were utilized to investigate the adsorption of phenol on pristine activated carbon (AC) and on activated carbon functionalized with OH, CHO, or COOH groups. Over the pristine AC, the phenol molecule undergoes weak physical adsorption due to van der Waals interactions between the aromatic part of the phenol and the basal planes of the AC. Among the three functional groups used to functionalize the AC, the carboxylic group was found to interact most strongly with the hydroxyl group of phenol. These results suggest that functionalized AC-COOH has great potential for use in environmental applications as an adsorbent of phenol molecules in aqueous phases.
ABSTRACT
The first step in the mechanism of n-butane oxidative dehydrogenation (ODH) on a V4O10 cluster and V4O10 supported SBA-15 is examined using DFT method. The activation and adsorption energies, oxidation state of V atoms are calculated. Over V4O10 the obtained results indicate that the activation of C-H bond of methylene group can occur at both the terminal and the bridging oxygen atoms with similar barrier (21.5-22.5 kcal mol(-1)). The role of SBA-15 (with and without modification by Al) in n-butane adsorption step has been studied in detail. SBA-15 itself has mild effect on the reaction process, but the substitution of silicon atoms by aluminum atoms results in an active supporter for V2O5 in ODH reaction. In that, the ratio of Si/Al will decide the direction of initial interaction steps between n-butane and catalyst surface and it will result in the selectivity of the reaction products.