ABSTRACT
Alloys or smelted metal mixtures have served as cornerstones of human civilization. The advent of smelted copper and tin, i.e., bronze, in the 4th millennium B.C. in Mesopotamia has pioneered the preparation of other metal composites, such as brass (i.e., mixture of copper and zinc), since the bronze age. The contemporary use of these alloys has expanded beyond using their physical strength. The catalytic chemistry of micron-scale brass or copper-zinc alloy can be utilized to effectively degrade emerging contaminants (ECs) in water, which are presenting significant risks to human health and wildlife. Here, we examine the photocatalytic activity of a commercially available micro-copper-zinc alloy (KDF® 55, MicroCuZn), made with earth abundant metals, for oxidative removal of two ECs. The micron-scale brass is independently characterized for its morphology, which confirms that it has the ß-brass phase and that its plasmonic response is around 475 nm. Estriol (E3), a well-known EC, is removed from water with ultraviolet (UV) radiation catalyzed by MicroCuZn and H2O2-MicroCuZn combinations. The synergy between H2O2, UV, and MicroCuZn enhances hydroxyl radical (ËOH) generation and exhibit a strong pseudo-first-order kinetic degradation of E3 with a decay constant of 1.853 × 10-3 min-1 (r 2 = 0.999). Generation of ËOH is monitored with N,N-dimethyl-4-nitrosoaniline (pNDA) and terephthalic acid (TA), which are effective ËOH scavengers. X-ray photoelectron spectroscopy analysis has confirmed ZnO/CuO-Cu2O film formation after UV irradiation. The second EC studied here is Δ9-tetrahydrocannabinol or THC, a psychotropic compound commonly consumed through recreational or medicinal use of marijuana. The exceptionally high solids-water partitioning propensity of THC makes adsorption the dominant removal mechanism, with photocatalysis potentially supporting the removal efficacy of this compound. These results indicate that MicroCuZn can be a promising oxidative catalyst especially for degradation of ECs, with possible reusability of this historically significant material with environmentally-friendly attributes.
ABSTRACT
A resource efficiency analysis was developed that evaluated photocatalyst loading and temperature inputs, and assessed hydroxyl radical (OH) production. Catalyst loading (Aeroxide® TiO2 P25) between 1 and 1500 mg L-1 and temperatures between 5 and 50 °C were analyzed as input resources for OH production. After, the best experimental conditions were used to degrade and mineralize estriol (E3). The analysis showed that a low catalyst concentration lead to poor absorption of radiation and a slow reaction. When high catalyst concentrations were tested, most of the radiation was absorbed, which produced results near the top of the slowing rate of OH generation. Temperature was found a relevant resource for increasing interfacial transfer to facilitate OH production following the Arrhenius model. Two indices to measure resource efficiency were proposed: 1) the OH generation index (OHI) and 2) the initial degradation efficiency (IDE). OHI was used to measure the efficiency of a catalyst using photonic flux to generate OH production. IDE evaluated the relationship between the photocatalytic reactor set-up, catalyst, and E3 degradation. It was observed that 1.18 OH was produced when a photon interacts with a photocatalyst particle when a load of 5 mg L-1 of photocatalyst is used at 20 °C. It was found that at initial time, 2.4 OH was generated in the systems to produce a degradation of one E3 molecule when using a photocatalyst load of 20 mg L-1 at 20 °C. Additionally, it was demonstrated that E3 mineralization was feasible under different catalyst loading scenarios.
