Send Orders of Reprints at reprints@benthamscience.net Micro and Nanosystems, 2013, 5, 3-13 3 1876-4037/13 $58.00+.00 © 2013 Bentham Science Publishers Large-scale Synthesis of Low-dimension Un-doped Iron Oxide Nanoparti- cles by a Wet-Chemical Method: Efficient Photo-catalyst & Sensitive Chemi-sensor Applications Mohammed M. Rahman a,b, *, Sher Bahadar Khan a,b , A. Jamal c , M. Faisal c , Abdullah M. Asiri a,b , Khalid A. Alamry a,b , Anish Khan a,b , Aftab Aslam Parwaz Khan a,b , Malik Abdul Rub a,b , Naved Azum a,b and Abdulrahman O. Al-Youbi b a Center of Excellence for Advanced Materials Research (CEAMR), King Abdulaziz University, Jeddah 21589, P.O. Box 80203, KSA; b Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, KSA; c Department of Chemistry and Center for Advanced Materials and Nano-Engineering (CAMNE), Faculty of Sci- ences and Arts, Najran University, P.O. Box 1988, Najran, 11001, KSA Abstract: Iron oxide nanoparticles (NPs) have been prepared in large-scale by wet-chemical method (150.0 o C and pH 8.33) using ferric chloride and urea as a starting materials in aqueous-alkaline medium. The structural, physical, and opti- cal properties are characterized using FT-IR, UV–vis spectroscopy, Raman spectroscopy, powder X-ray diffraction, Field- emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and Electron diffraction sys- tem (EDS). The NPs size (average dia. 45 ± 5 nm) was measured by FE-SEM while the single phase of NPs were exem- plified using powder X-ray diffraction technique. As-grown nanoparticles were applied for the photocatalytic degradation using acridine orange (ACR) and chemical sensing of aqueous ammonia. Almost 58.38% degradation with ACR was ob- served in presence of nanoparticles under UV sources (250 W). The silver electrode (AgE, surface area, 0.0216 cm 2 ) was immobilized with NPs which enhanced ammonia-sensing performances in their electrical response (I-V characterization) for detecting and quantifying the ammonia in aqueous system. The analytical performances of NPs sensor were investi- gated that the sensitivity and stability of the sensor improved extensively using NPs thin-film on active silver surface. The calibration plot was linear (R =0.9337) over the large range of 5.0 M to 0.5 M. The sensitivity was calculated as 4.6154 Acm -2 mM -1 with detection limit (2.5±0.2 M), based on a signal/noise ratio ( 3N / S ). This study has introduced a novel way for efficient chemical sensor development as well as active photo-catalyst using low-dimensional NPs for the detec- tion of environmental carcinogenic and hazardous compounds. Keywords: Iron oxide nanoparicles, Chemi-sensors, Sensitivity, Solution method, Optical properties. 1. INTRODUCTION Low-dimensional un-doped metal oxide nanostructures have been prepared using simple and reliable synthesis method in terms of reaction parameters, chemical compo- nents, and controlled morphologies, which greatly influenced the properties of nano-materials [1-3]. Nano-sized and nano- structures of iron oxides have explored comprehensively because of their widespread applications [4,5] such as ferro- fluids, magnetocaloric refrigeration, biotechnology and in- vivo biological field [6-8]. These un-doped nanomaterials proposed various applications in biomaterials [9, 10] and biomedical [11, 12] fields, which magnetically controlled drug delivery, magnetic resonance imaging as contrast agent, tissue-repair, and detoxification of natural fluids [13-20]. Metal oxide nanoparticle is also implemented in different technological aspects such as biomedical imaging, drug de- livery, photo-catalysis, and other biological applications *Address correspondence to this author at the Center of Excellence for Advanced Materials Research (CEAMR) & Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia; Tel: +966-596421830; E-mail: mmrahman@kau.edu.sa [21, 22]. Reducing the crystal shape and size, and increasing the active surface area of the sensing materials are an effi- cient way to increase the sensing signals [23]. In catalysis, the photo-degradation of textile organic dyes was studied in wastewater treatment in aqueous phase due to their non-biodegradable nature. The typical mineralization techniques were used as adsorption using activated carbon and coagulation by coagulants, hardly transform the aqueous organic dye to the solid phase, leaving the pollutant undes- troyed [24, 25]. Recently researchers have studied the photo- catalytic degradation of toxic organic dyes using photo- catalysts usually with semiconducting materials (i.e., tita- nium oxide, zinc oxide, cobalt oxide, cerium oxide) in UV/visible and xenon beams [26-30]. Our attempt was to study the photo-catalytic degradation of organic dye (water soluble, Acridine Orange) with as-grown iron oxide nanopar- ticles in aqueous system under 250W Mercury lamp. The mechanism constituted heterogeneous photo-catalytic oxida- tion has been performed thoroughly in this study. When a semiconductor (MO x ) absorbs a photon of energy equivalent to or greater than its band gap width, an electron