No abstract

Arsenic is a carcinogenic substance, with many cases of poisoning related to arsenic pollution in groundwater. In Taiwan arsenic in groundwater caused the notorious Blackfoot disease. Methods for arsenic removal from water include precipitation, membrane processes, ion exchange, and adsorption, but these processing technologies suffer from high investment costs and complex operations. The traditional adsorption method cannot be used for arsenic removal due to its high operating costs, difficulties in recovery, and low adsorption capacity. To address these issues, this study designed an adsorption material based on biochar for arsenic removal with higher adsorption properties and easy recovery. Biochar sources are readily available from waste wood as a cheap and environmentally friendly material. The efficiency of As (III) removal is also promoted by FeCl3 and KMnO4. The objectives of this research are to obtain optimum operation conditions by assessing the effects of different iron and manganese contents, different doses, different pH and different initial concentration. The adsorption mechanism between As (III) and biochar was studied by adsorption isotherms and the kinetic model. X-ray diffraction, energy-dispersive X-ray spectroscopy and elemental analyzer analysis results show that modified biochar has major elements of Fe and Mn. There is greater magnetism, 40 emu g− 1, in the modified biochar. The maximum adsorption efficiency of 81% and 0.72 mg g− 1 capacity occurs when the ratio of Mn, Fe and C is 4:1:1. The adsorption capacity is high under higher pH with pristine biochar and 1FeC under lower pH with 1Fe2MnC. The reaction mechanism is divided into four pathways. The first pathway is the attachment of As (III) ions into the pore of biochar via physical adsorption. In the second pathway, biochar can connect with As (III) through hydrogen bonding from the function group -OH in the biochar and the As (III) itself. In the third pathway, they can contact each other by electron force when the biochar surface is filled with a positive charge. In the fourth pathway, the compounds of manganese have strong oxidizability to oxidize As (III) to As(V). The iron ions then act as a bridge connecting the biochar and the As (III), resulting in the formation of new complex compounds.

This study novel-designed sludge biochar (SB) adsorbed for arsenic removal with lower operating costs and higher adsorption efficiency properties. Generally, biochar only relies on micropores for pollutant adsorption, but physical adsorption is not highly efficient for arsenic removal. Therefore, in order to improve the removal efficiency of arsenic by SB, diethylenetriamine (DETA) and FeCl3 were used in this study to modify the surface of SB by an immersion method. The objectives of this research are to obtain optimum operation conditions by assessing the effect of different Fe content, pH and initial concentration on adsorbing arsenic. This study is the first to use Density Functional Theory (DFT) to simulate and verify the adsorption mechanism of arsenic by SB. Results showed the presence of amine/iron oxyhydroxides functional greatly promoted SB surface activity and its arsenic adsorption potential. The surface area, pore volume and pore size of the SB were estimated to be 525 m2 g−1, 0.35 cm3 g−1 and 8.71 nm, respectively. DFT model result is the same as the result of arsenic adsorption performance with the high adsorption energy (−246.3 kJmol−1) and shorter bond distances (1.42 Å), indicating strong chemical adsorption between arsenic and material. The reaction mechanism is divided into four pathways, including oxidation-reduction, complexation, electrostatic adsorption and pore adsorption.

Multilayer ZnO sheet-like flakes were synthesized by a simple method of precipitation and characterized by the techniques of X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The findings are proven that the SEM images show the overall morphology of a single sheet-like ZnO nanostructure made from uniformly thick nano-sheets. In an aqueous environment, the acoustic ability of the prepared material was assessed using ultrasound (US) radiation to degrade oxytetracycline (OTC) and norfloxacin (NF). To increase the degradation efficiency, a US/ZnO/peroxodisulfate system was developed by introducing ammonium persulfate ((NH4)2S2O8) and sodium persulfate (Na2S2O8), exhibiting excellent synergistic effects. Result show the decomposition efficiency for NF removal with Na2S2O8 (64%) appeared to be slightly better than with (NH4)2S2O8 (56%). By contrast, the ultrasonic catalytic efficiency of Na2S2O8 (98%) was slightly better than that of (NH4)2S2O8 (94%) for OTC removal. The addition of scavengers to the US/ZnO/peroxodisulfate system through the NF and OTC results in the largest effect of holes. The degradation is considered to be often caused by holes. In this system, the Na2S2O8 can have two roles to increase the rate of degradation: (1) The SO4− formed by Na2S2O8 under ultrasonic irradiation directly degraded to norfloxacin on ZnO surface; and (2) S2O82- behaved as an electron acceptor, inhibiting recombination of electron hole pairs, enabling the development of more ·OH. Therefore, the synergistic effect significantly increases US/ZnO/peroxodisulfate sonocatalytic activity (Hu, S.B., et al., 2017. Aqueous norfloxacin sonocatalytic degradation with multilayer flower-like ZnO in the presence of peroxydisulfate. Ultrasonics Sonochemistry, 38(1), pp.446–454).

Waste recycling and reuse will result in significant material and energy savings. In this research, usage of hospital sludge as a biochar adsorbent for wastewater treatment plants was investigated. Microwave carbonization was used to carbonize the sludge and then chemically activated with ZnCl2to increase surface area and porosity. A newly designed iron metal doped sludge biochar carbon (SBC) has effective adsorption of inorganic arsenic (As(III), As2O3) in water. The findings clearly demonstrate the viability and utility of using hospital sludge as a source of carbon to generate SBC. The adsorption mechanism of As(III) on SBC’s iron-metal-modified surface has been studied using density functional theory (DFT) to understand the impact of functional complexes on adsorption As(III). Tests showed physical as well as chemical adsorption of As(III) on Fe-SBC surface. Fe’s involvement in functional complexes greatly fostered SBC surface activity and it’s As(III) adsorption ability. The physical adsorption energies of As(III) with Fe functional complexes on the SBC surface were −42.3 KJ mol−1. Other hand, the chemical adsorption energies of As(III) on Fe-SBC surface was −325.5 KJ mol−1. As(III) is capable of interacting in a bidentate fashion with the dopants through the protonated oxygen atoms and this conformation of the cyclic structure is higher in the adsorption energy than the others.