Joseph Auresenia

Biodegradability and toxicity assessment of trans-chlordane photochemical treatment.

The removal of trans-chlordane (C(10)H(6)Cl(8)) from aqueous solutions was studied using UV, UV/H(2)O(2), UV/H(2)O(2)/Fe(2+), UV/TiO(2), or UV/TiO(2)/H(2)O(2) treatment using either UV/Vis blue lamps or UVC lamps (254 nm). H(2)O(2), FeSO(4) and TiO(2) were added at 1700, 456, and 2500 mgL(-1), respectively. trans-Chlordane was not significantly removed in non-irradiated controls and in samples irradiated with UV/Vis. It was also not removed in the absence of surfactant Triton X-114 added at 250 mgL(-1). In the presence of the surfactant, trans-chlordane concentration was reduced by 95-100% after 48 h of UVC and UVC/H(2)O(2) treatments and 70-80% after UVC/H(2)O(2)/Fe(2+), UVC/TiO(2) and UVC/H(2)O(2)/TiO(2) treatments. Based on these results, UVC, UVC/H(2)O(2) and UVC/TiO(2) treatments were further investigated. UVC treatment supported the highest pollutant removal (100% in 48 h), dechlorination efficiency (81% in 48 h), and detoxification to Lepidium sativum seed germination and activated sludge respiration although irradiated samples remained toxic to Chlorella vulgaris. Biodegradation of the UVC irradiated samples removed the source of algae toxicity but this could not be clearly attributed to the removal of trans-chlordane photoproducts because the surfactant interfered with the chemical and biological assays. Evidence was found that trans-chlordane was photodegraded through photolysis causing its successive dechlorination. trans-Chlordane removal was well described by a first order kinetic model at a rate of 0.21±0.01h(-1) at the 95% confidence interval.

Effect of Cu on Ni Catalyst for the Thermal Decomposition of Methane: A Molecular Dynamics Investigation

investigated via ab initio DMol 3 molecular dynamics simulation. Initial simulation used the Local Density Approximation (LDA) with the Perdew-Wang 1992 (PWC) specific local exchange correlation functional, Gaussian double zeta plus polarization function basis set (DNP) at gamma (1x1x1) k-point calculation and orbital cut-off of 3.4 A, with additional parameters: T = 1300K, time step = 2.5 fs, simulation time of 0.25 ps, with canonical NVT (constant amount (N), volume (V) and temperature) thermodynamic ensemble and Generalized Gradient Moment (GGM) thermostat. Results demonstrate the capacity of Ni for carbon deposition, whereas the addition of Cu resulted in the following: promoted the disjoining of the H atoms from the C atom allowing the C atom to form more bonds with the metal surface; accelerated the initial catenation of the CH4 atom (Ni = 12.5 fs; Ni-Cu = 10.0 fs); and delayed the initial deposition of C atom on the metal surface (Ni = 30.0 fs; Ni-Cu = 37.5 fs). Examination of the decomposition mechanism revealed the initial formation of a metal-H bond between one of the H atoms of the CH4 molecule and one of the metal atoms, followed by the re-formation of a transition bond between the C atom and the H atom bonded to the metal. This brings the C atom towards the metal surface for deposition after which the transition C-H bond is broken. This implied role of hydrogen in the deposition of carbon agrees with experimental results in literature.

CNT Production through the Catalytic Decomposition of Methane on Ni-Cu/γ-Al2O3 at Varying Ni-Cu Ratios: An Ab Initio and Empirical Investigation

The decomposition of a single CH4 molecule on Ni-Cu/γ-Al2O3 catalyst surface with varying Ni-Cu ratios for CNT production was determined through ab initio calculations with experimental verification. The structural model was based on empirical XRD characterization data from experimentally-prepared catalysts. Structural relaxation and ab initio molecular dynamics simulations were performed using Materials Studio 2016 DMol with the Local Density Approximation – Vosko-Wilk-Nusair (LDA-VWN) exchange correlation functional, Gaussian double zeta plus polarization function basis set (DNP) at 2 × 2 ×1 k-point calculation and orbital cut-off of 3.5 Å, with simulation parameters: T = 1,148 K, time step = 1.9 fs (78.5 a.u.), simulation time of 0.38 ps, with the canonical NVT (constant amount (N), volume (V) and temperature (T)) thermodynamic ensemble and Generalized Gaussian Moment (GGM) thermostat. Ab initio simulation data predicted a decrease in C deposition time with 1:1 Ni-Cu/γ-Al2O3. Empirical data from TGA and SEM analyses confirmed higher CNT yield on 1:1 Ni-Cu/γ-Al2O3. Ab initio calculations indicated an increase in binding energy magnitude with the formation of a Ni-Cu alloy. This increase in energy is attributed to the calculated decrease in crystal size, and was verified by the decrease in average CNT diameter produced on 1:1 Ni-Cu/γ-Al2O3. These findings demonstrate the viability of CTDM as a technology for CNT production, as well as its adaptability to simpler catalytic systems for industrial or commercial applications.