www.afm-journal.de FULL PAPER © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 www.MaterialsViews.com wileyonlinelibrary.com 1. Introduction Arsenic contamination in natural water is a global threat due to its high toxicity and carcinogenicity. [1–5] Long-term exposure to arsenic-polluted water may result in some negative effects on human health and cause several diseases, such as lungs, bladder, kidneys and skin cancer. [2,4,6] Arsenic in even very low concentrations can still have a strong adverse effect on health, the maximum contaminant level (MCL) of arsenic in drinking water is suggested to be 10 μg L -1 instead of the previous limit of 50 μg L -1 according to the guideline of World Health Organization (WHO). [7] However, numerous water bodies around the world carry soluble arsenic at concentrations higher than this standard. The arsenic concentration of many ground waters in the western United States is found higher than 10 μg L -1 , [5] and most tube- wells in South and Southeast Asia do not meet the standard of WHO. [6] To meet the stricter standard of 10 μg L -1 , a simple approach for efficient arsenic removal at low concentrations from drinking water is required. Arsenic mainly exists as arsenite (As (III)) and arsenate (As (V)) in natural water. [8] As (V) is the predominant spe- cies under oxidizing conditions and As (III) predominates in moderately reducing environments such as groundwater. [4] Generally, both species are present in water simultaneously. Compared to As (V), As (III) is more toxic and it is generally accepted that it is more difficult to be removed due to its low affinity to various adsorbents. [9,10] To achieve effective As (III) removal, it is required to pre-treat As (III) by oxidizing it to As (V) and/or adjust the pH value before coagulation–precipita- tion/adsorption processes. [9,11–13] Apparently, the pre-treatment increases the operation cost and causes secondary pollution problems, thus it is disadvantageous for practical applications. It is highly desirable to develop an adsorbent for efficient and cost-effective removal of both As (V) and As (III) without any pre-treatment. During the past decades, several techniques have been developed in the removal of arsenic from the wastewater, including precipitation followed by solid/liquid separation, adsorption and ion exchange, biological removal processes, and so forth. [2] Due to the low cost, good performance and easy operation, adsorption is considered to be one of the most effec- tive approaches among these technologies. Iron oxide-based materials have been widely used in arsenic removal because of their low cost, natural abundance and effective performance for both As (V) and As (III) removal. However, the adsorption High-Content, Well-Dispersed γ-Fe 2 O 3 Nanoparticles Encapsulated in Macroporous Silica with Superior Arsenic Removal Performance Jie Yang, Hongwei Zhang, Meihua Yu, Irene Emmanuelawati, Jin Zou, Zhiguo Yuan, and Chengzhong Yu* Novel composites of iron oxide encapsulated in macroporous silica with excellent arsenic adsorption performance have been successfully developed. Macroporous silica foams with large pore sizes of ≈ 100 nm and a high pore volume of 1.6 cm 3 g -1 are chosen as the porous matrix. Electron tomography technique confirms that γ-Fe 2 O 3 nanoparticles with an average particle size of ≈ 6 nm are spatially well-dispersed and anchored on the pore walls at even a high γ-Fe 2 O 3 content of 34.8 wt%, rather than forming aggregates inside the pores or on the external surface. The open large-pore structure, high loading amount, and the non-aggregated nature of γ-Fe 2 O 3 nanoparticles lead to increased adsorption sites and thus high adsorption capacities of both As (V) and As (III) without pre-treatment (248 and 320 mg g -1 , respectively). Moreover, the composites can reduce the concentration of both As (V) and As (III) from 100 to 2 μg L -1 . It is also demonstrated that the composites can be applied in a household drinking water treatment device, which can continuously treat 20 L of wastewater containing As (V) with the effluent concentration lower than the World Health Organization standard. DOI: 10.1002/adfm.201302561 J. Yang, H. W. Zhang, M. H. Yu, I. Emmanuelawati, Prof. C. Z. Yu Australian Institute for Bioengineering and Nanotechnology The University of Queensland Brisbane, QLD, 4072, Australia E-mail: c.yu@uq.edu.au Prof. J. Zou Materials Engineering and Centre for Microscopy and Microanalysis The University of Queensland Brisbane, QLD, 4072, Australia Prof. Z. G. Yuan Advanced Water Management Centre The University of Queensland Brisbane, QLD, 4072, Australia Adv. Funct. Mater. 2013, DOI: 10.1002/adfm.201302561