_applied sciences_  
_Article_  
Investigation of the Thermodynamics for the Removal of As(III) and As(V) from Water Using Synthesized ZnO Nanoparticles and the Effects of pH, Temperature, and Time  
[PERSON] 1,2, [PERSON] 1, [PERSON] 1, [PERSON] 3\({}^{\text{(\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{ \text  
thus inhibiting the formation of adenosine triphosphate and interfering with normal cell function [3; 14]. Acute exposure to high doses of arsenic is known to cause health problems such as hyperkeratosis, cutaneous malignant tumors, alopecia, peripheral neuropathy, anemia, and skin cancer [1; 2; 3; 14; 15]. In order to reduce the risk of As exposure, numerous countries have adopted a 10 \(\mathrm{\SIUnitSymbolMicro g}\)/L limit as their drinking water standard, while other countries have maximum As limits at 50 \(\mathrm{\SIUnitSymbolMicro g}\)/L [2; 7; 16; 17; 18; 19]. The removal of arsenic from aqueous solutions has been shown to be dependent on the oxidation state, concentration, pH, and ionic strength. Arsenic removal from water has been achieved using technologies such as membrane technology, adsorption, ion exchange, coagulation/ flocculation, reverse osmosis, electrochemical, and bioremediation [20; 21; 22; 23; 24; 25; 26; 27; 28; 29]. However, many of these technologies are ineffective or inefficient, and cost-prohibitive [30]. There has been increased interest in adsorption methods due to their cost and lack of by-products. Typically, adsorbents can be recycled, and process operation can be flexible [4; 22]. Recently, the use of nanosorbents has become of interest due to their high surface area to volume ratio, the high number of active sites, and strong reactivity. The most studied nanoparticles to remove As from water include: metal oxides, metallic, bimetallic, zeolites, ferrite, polymers, activated alumina, and activated carbon [4; 22; 31]. Various metal oxides based nanosorbents for arsenic remediation have been prepared, which include Fe\({}_{2}\)O\({}_{3}\), Fe\({}_{3}\)O\({}_{4}\), Mn\({}_{3}\)O\({}_{4}\), MnFe\({}_{2}\)O\({}_{4}\), and ZnO [4; 32; 33; 34; 35; 36]. As well, mixed metal oxide materials such as Fe-Ce, Fe-Mn, Fe-Ti, Ce-Ti, Fe-Zr, Fe-Cu, Mn-Co, and Fe-Cr have been synthesized and tested for As adsorption [4; 32; 33; 34; 35; 36]. [PERSON] et al. found that acetate-functionalized ZnO particles effectively removed arsenic from 2000 ppb to less than 10\(\mathrm{\SIUnitSymbolMicro g}\)/L [37]. [PERSON] and [PERSON] studied the adsorption of Cd(II), Pb(II), As(III), and Se(IV) using ZnO nanoflowers in multi-metal systems using an adsorption dose of 0.8 \(\mathrm{g}\)/mL [38]. The removal efficiency was 57% for Cd(II) and 99% for Pb(II). Cu (II), As(III), and Se(IV) adsorption efficiencies were greater than 75% [38], whereas [PERSON] et al. found that ZnO nanoparticles removed up to 88.57 \(\mathrm{m}\mathrm{g}\)/\(\mathrm{g}\) of Cr(III) ions under optimal reaction conditions [39]. [PERSON] et al. investigated the binding of As(III) and As(V) to Fe\({}_{7}\)S\({}_{8}\) and showed a pH-independent binding process and approximately 100% binding of both ions from pH 3 through pH 6 [40]. [PERSON] et al. developed Fe\({}_{3}\)O\({}_{4}\), Mn\({}_{3}\)O\({}_{4}\), and FeMn\({}_{2}\)O\({}_{4}\) nanomaterials for the removal of As(III) and As(VI) from solution [30]. The Fe\({}_{3}\)O\({}_{4}\), Fe\({}_{2}\)MnO\({}_{4}\), and Mn\({}_{3}\)O\({}_{4}\) showed binding capacities of 0.0323, 0.7182, and 0.0089 \(\mathrm{m}\mathrm{g}\)/\(\mathrm{g}\) for As(III), respectively, whereas the binding of As(V) from aqueous solution showed capacities of 1.575, 2.125, and 0.212 \(\mathrm{m}\mathrm{g}\)/\(\mathrm{g}\) for the Fe\({}_{3}\)O\({}_{4}\), Fe\({}_{2}\)MnO\({}_{4}\), and Mn\({}_{3}\)O\({}_{4}\), respectively. [PERSON] et al. investigated the binding of As(III) and As(V) to Fe\({}_{3}\)O\({}_{4}\) and Fe\({}_{2}\)O\({}_{3}\) nanomaterials, which showed pH-independent binding of both As(III) and As(V) from pH 6-10 [41].