This review presents an introduction to the synthesis of metallic nanoparticles by radiation-induced method, especially gamma irradiation. This method offers some benefits over the conventional methods because it provides fully reduced and highly pure nanoparticles free from by-products or chemical reducing agents, and is capable of controlling the particle size and structure. The nucleation and growth mechanism of metallic nanoparticles are also discussed. The competition between nucleation and growth process in the formation of nanoparticles can determine the size of nanoparticles which is influenced by certain parameters such as the choice of solvents and stabilizer, the precursor to stabilizer ratio, pH during synthesis, and absorbed dose.

19Current study reports the facile synthesis of Ag/MoS 2 nanocomposite 20 photocatalyst for visible-light driven hydrogen gas evolution. The MoS 2 nanoflakes 21 were hydrothermally prepared and then decorated with Ag nanoparticles (NPs) by 22 simple chemical reduction process at room temperature. Detailed 23 characterizations had been carried out to probe the physical structure and 24 properties of the as-synthesized nanocomposite. The nanocomposite shows 25 enhanced visible-light absorption and pronounced quenching of 26 photoluminescence intensity as compared to that of pure MoS 2 . The 27 photocatalytic hydrogen gas evolution experiments reveal that the Ag NPs can act 28 as efficient co-catalyst for MoS 2 nanoflakes and subsequently improve the 29 hydrogen gas evolution rate. Ag-loading dependent photocatalytic tests indicate 30 that the 20 wt%-Ag/MoS 2 nanocomposite exhibits the highest photocatalytic 31 activity with hydrogen gas evolution of 179.5 µmol H 2 /g cat , which is enhanced by 32 95% if compared to that of commercial MoS 2 nanopowder (92.0 µmol H 2 /g cat ). The 2 possible mechanisms that contribute to the improvement of visible-light driven 34 photocatalytic performance for nanocomposite are proposed. 35 36Instead, the excitons that formed upon absorbing incident photon can further split 62 the water molecules into its constituents. Therefore, photocatalysis hydrogen 63 3 generation through suspension remain attractive since it is well-complement with 64 the worldwide initiative toward the implementation of the technology, which is 65 anticipated to fully harness the sunlight from mother nature as one of highly 66 abundance natural resource. 67As part of two-dimensional materials, graphene also has gained significant 68 popularity for photocatalysis applications, where it has been greatly used as 69 matrix that is able in prolong the charge-carrier lifetimes. 7 In contrast to the 70 graphene, MoS 2 appear to be a semiconductor by itself and had been repeatedly 71 proved to exhibit tunable bandgap energy that is strictly dependent on the atomic 72 thickness. The bandgap values can be maneuvered from 1.9 eV (direct bandgap) 73 for a single layer MoS 2 nanosheet, down to 1.2 eV (indirect bandgap) for 74 multilayer MoS 2 nanoflakes, in which both of these bandgap are well-correspond 75 to the light absorption in the visible-(450-700 nm) and infrared-region (700-1400 76 nm), respectively. 8 As a result, MoS 2 would become one of the ideal candidates to 77 be used as visible-and infrared-active optical material for photo-energy 78 engineering including photosplitting of water. 79 In terms of the structural characteristic, MoS 2 generally exists in expanded 80 two-dimensional sheet-like structure 8, 9 . Such expanded planar nature not only 81 renders highly-exposed surface area for it, but it is also propitious to be employed 82 as a matrix in supporting other inorganic nanoparticles (NPs) to form new class of 83 nanocomposite with value added features that are highly-suitable for specific 84 application...

A novel optical detection system consisting of combination of uricase/HRP-CdS quantum dots (QDs) for the determination of uric acid in urine sample is described. The QDs was used as an indicator to reveal fluorescence property of the system resulting from enzymatic reaction of uricase and HRP (horseradish peroxidase), which is involved in oxidizing uric acid to allaintoin and hydrogen peroxide. The hydrogen peroxide produced was able to quench the QDs fluorescence, which was proportional to uric acid concentration. The system demonstrated sufficient activity of uricase and HRP at a ratio of 5U:5U and pH 7.0. The linearity of the system toward uric acid was in the concentration range of 125-1000 µM with detection limit of 125 µM.

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In this study, porous silicon (PSi) was prepared and tested as an extended gate field-effect transistor (EGFET) for pH sensing. The prepared PSi has pore sizes in the range of 500 to 750 nm with a depth of approximately 42 µm. The results of testing PSi for hydrogen ion sensing in different pH buffer solutions reveal that the PSi has a sensitivity value of 66 mV/pH that is considered a super Nernstian value. The sensor considers stability to be in the pH range of 2 to 12. The hysteresis values of the prepared PSi sensor were approximately 8.2 and 10.5 mV in the low and high pH loop, respectively. The result of this study reveals a promising application of PSi in the field for detecting hydrogen ions in different solutions.

Magnetically recyclable 3D CoFe2O4–TiO2 photocatalyst nanocomposite.

Wollastonite was produced using solid-state reaction from limestone and silica sand. Limestone containing a high percentage of CaO (55.10%) and silica sand with 99% SiO 2 were used as starting materials. The ratios of limestone/sand used were 1:1, 2:1 and 3:1 with various firing temperatures, namely 1100, 1200, 1300, 1400 and 1450 • C. The raw materials and fired products were characterised for mineral phases, chemical composition of content such as CaO, SiO 2 and loss on ignition (LOI), density and microstructure. CaSiO 3 with an ␣-phase was detected at firing temperatures as low as 1300 • C, together with olivine and quartz phases, obtained from a 1:1 ratio. No ␣-CaSiO 3 was detected for 2:1 and 3:1 ratios; only olivine and larnite phases were present. The density of the product was 2.93 g cm −3 , which is close to the theoretical value, with a specific surface area of 3.23 m 2 g −1. This study shows that the Malaysian limestone and silica sand can produce good properties of wollastonite materials.

Colloidal Fe3O4 nanoparticles were synthesized using a gamma-radiolysis method in an aqueous solution containing iron chloride in presence of polyvinyl alcohol and isopropanol as colloidal stabilizer and hydroxyl radical scavenger, respectively. Gamma irradiation was carried out in a 60Co gamma source chamber at different absorbed doses. Increasing the radiation dose above a certain critical dose (100 kGy) leads to particle agglomeration enhancement, and this can influence the structure and crystallinity, and consequently the magnetic properties of the resultant particles. The optimal condition for formation of Fe3O4 nanoparticles with a uniform and narrow size distribution occurred at a dose of 100 kGy, as confirmed by X-ray diffractometry and transmission electron microscopy. A vibrating sample magnetometry study showed that, when radiation dose increased, the saturation and remanence magnetization decreased, whereas the coercivity and the remanence ratio increased. This magnetic behavior results from variations in crystallinity, surface effects, and particle size effects, which are all dependent on the radiation dose. In addition, Fourier transform infrared spectroscopy was performed to investigate the nature of the bonds formed between the polymer chains and the metal surface at different radiation doses.