Contents lists available at ScienceDirect Physica B journal homepage: www.elsevier.com/locate/physb The effect of saturation magnetization of nanocatalyst and oscillating magnetic field for green urea synthesis Noorhana Yahya ⁎ , Bilal Alqasem, Muhammad Irfan, Saima Qureshi, Zia Ur Rehman, Afza Shafie, Hassan Soleimani Fundamental and Applied Sciences Department, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak, Malaysia ARTICLE INFO Keywords: α-Fe 2 O 3 Nanowires Nanocatalyst Singlet to triplet conversion Green urea Oscillating magnetic field ABSTRACT Hematite and cupric oxide nanowires have been synthesized using the oxidation method for green urea production. Hematite nanowires were obtained by the oxidation of an iron wire at a temperature of 650 °C and ambient pressure in the presence of N 2 and O 2 gases. Cupric oxide nanowires were obtained by the same method at 700 °C, using a copper wire. The X-ray diffraction results show the formation of rhombohedral structure of α-Fe 2 O 3 and monoclinic phase of CuO. FE-SEM results reveal the formation of nanowires with dimensions ranging between 5–15 μm and 4–12 μm in length and a diametere ranging between 50–150 nm and 50–250 nm for α-Fe 2 O 3 and CuO respectively. The VSM results show that the saturation magnetization values for hematite and cupric oxide were 132.8700 and 0.0124 emu/g, respectively. The nanowires were used as catalyst for green urea synthesis in the presence of an oscillating and a static magnetic fields. The use of nanocatalyst with high saturation magnetization gives a higher yield of urea due to the increase in the singlet to triplet conversion. The highest yield of urea 11243 ppm was achieved by applying an oscillating magnetic field of frequency 0.5 MHz and using α-Fe 2 O 3 nanowires as nanocatalyst. 1. Introduction It has been observed that nanoscale materials are quantum confined thus size reduction from bulk changes the band gap and electronic properties. The high surface to volume ratio and high surface charges make them suitable candidate for use as catalyst in chemical reaction [1]. The sharp tips of 1D nanostructures can effectively enhance local electric fields and magnetic fields [2]. The hematite (α- Fe 2 O 3 ) nanowires have recently attracted considerable attention be- cause of its low cost, high stability, nontoxicity, environment friendli- ness and have high resistance to corrosion [3]. α-Fe 2 O 3 is an n-type semiconductor with a band gap of 2.1 eV which is the most stable iron oxide under ambient conditions [4]. Hematite nanostructures have numerous applications in fabrication of transistors [5], sensors [6], catalysts [7–11], pigments [12], rechargeable lithium batteries [13], water splitting and treatment [14]. Various α-Fe 2 O 3 nanostructures, such as 0D (particles) [15], 1D (rods, spindles, wires, tubes, and belts) [16–19], 2D/3D (rings, disks, dendrites, flowers, mesoporous and cubes) [20–22], and hybrids, have already been fabricated by a variety of methods [23]. Copper oxide (CuO) is a p-type semiconductor and gains considerable attentions because of its excellent electrical and optical properties [24,25]. CuO with narrow band gap of 1.2 eV is extensively used in various applications such as sensors [26,27], field emitters [28], solar cells [29], splitting of water [30], coating [31] and catalysis [32–37]. To date, there are diversified copper oxide nanos- tructures with various shapes including nanoparticles, nanowires, nanotube, nanoribbon bundles, nanoplates, nanospheres, honeycombs, hierarchical and flowerlike [38–46]. CuO nanostructures have been fabricated by several methods such as wet chemical method [47], aqueous solution decomposition [48], hydrothermal route [49], micro- wave hydrothermal [50] and thermal oxidation method [51]. The size and morphology of nanocatalyst affect the chemical and physical properties and hence its application [52]. Scientists have shown special concern in studying the effect of an external magnetic field on the rates of chemical reactions and related processes [53–55]. The yield of chemical reaction is greatly influenced by magnetic field [56]. This influence is due to transitions between singlet and triplet states of reactants caused by modification of their reaction rates [57,58]. The rate of chemical reaction and extent of spin mixing can be altered either by energetically separating the triplet sublevels via Zeeman interaction with static magnetic fields of typically 1mT or more, or by improving the mixing process through the application of low static magnetic fields [59]. The effect of oscillating magnetic field on chemical reaction, theoretically and experimentally http://dx.doi.org/10.1016/j.physb.2016.11.024 Received 5 October 2016; Received in revised form 13 October 2016; Accepted 20 November 2016 ⁎ Corresponding author. E-mail addresses: noorhana_yahya@petronas.com.my (N. Yahya), bilalalqasem@yahoo.com (B. Alqasem). Physica B 507 (2017) 95–106 0921-4526/ © 2016 Elsevier B.V. All rights reserved. Available online 29 November 2016 crossmark