All chemicals used in the present study were of pure grade (Aldrich or Merck) and were used without further purification. Silver nitrate (>99.95%, Sigma), potassium chloride and potassium bromide; KCl, KBr, >99.5%, Merik Chemical A. R. and Polyvinylpyrrolidone (PVP, average MW = 40,000, 30 mg/mL, Sigma) were used as received, without additional purification. Bi-distilled water was used whenever water is used.

Preparation of silver halide (AgX)

Silver chloride Nanoparticulate (AgCl NP) was prepared by titrating 500 mL aqueous solution of KCl (0.02 M) drop wisely to 100 mL aqueous solution of AgNO₃ (0.01 M) mixed with a solution of polyvinylpyrrolidone (PVP) at room temperature. The solution mixture was stirred continuously for about three hours keeping the reaction vessel in a dark place to prevent the formation of metallic Ag⁰. Precipitation was achieved immediately and the formed precipitate was isolated and washed three times with bidistilled water then finally with acetone to expel water from the surface. The solid product was dried at 60˚C for ≈ 6 hours then grinned in an agate mortar into a fine powder and stored in an amber vial since AgCl is known to be photosensitive. Synthesis of silver bromide Nanoparticulate (AgBr NP) was performed via the same procedure using KBr instead of KCl as a precursor.

1) FTIR spectra: were recorded on a Nicolet iSio FT-IR spectrophotometer in the 4000 - 400 cm⁻¹ region using KBr disk technique (Chemistry department, Faculty of science, Benha University, Egypt).

2) Thermal analysis: Thermogravimetric analysis (TGA-DTG) were carried out using Shimadzu TGA-50H thermal analyzer within the temperature range 25˚C - 800˚C (Central Lab, Faculty of Science, Ain Shams University, Cairo, Egypt). All measurements were done under nitrogen atmosphere at heating rate of 10˚C/min.

3) Electronic spectra: Electronic spectra of nanoparticles were measured in the solid state (Nujol Mull technique) using Jasco V-530 (UV-Vis) double beam spectrophotometer (Japan) with scanning speed 400 nm/min and band width 2.0 nm using 10 mm matched quartz cell at room temperature in the range 800 - 200 nm at Faculty of Science, Benha University, Benha, Egypt.

4) X-ray diffraction: X-ray diffraction analysis (XRD) was carried out using SIEMENS D5000 instrument. The patterns were run with Cu-filtered CuK_α radiation of wavelength 1.79 A˚ energized at 45 kv and 10 mA. The sample was measured at room temperature in the range of 2θ from 20˚ - 80˚.

5) High resolution transmission electron microscopy: The morphology and particle shape of the as-prepared samples were studied by high resolution transmission electron microscopy (HRTEM) using JEOL TEM 2100 high resolution electron microscope at 100 kv by dispersed sample in ethanol on a copper grid.

6) Energy dispersive X-ray (EDX): The energy dispersive X-ray spectroscopy (EDX) was measured with a Horiba EMAX X-act energy dispersive spectroscopy that was attached to the Hitachi S-4800 system.

The antimicrobial susceptibilities against two Gram-positive bacteria (Bacillus cereus, Staphylococcus aureus) and four Gram-negative bacteria (Salmonella typhi, Escherichia coli, P. aeruginosa and Klebsiella pneumoniae) in addition to five fungi (Aspergillus flavus, A. carbonarus, Penicillium verrucosum, Fusarium verticelloides, and A. niger) (Salmonella typhi, Escherichia coli, P. aeruginosa and Klebsiella pneumoniae) were tested by the disk diffusion technique developed by Bauer et al. [26] and described in our previous work [27] . The method is based on the determination of an inhibited zone proportional to the bacterial susceptibility to the antimicrobial present in the disk. Three replicas were made for each treatment to minimize error.

For a typical photocatalytic experiment, 50 mg of (AgX NP) was added to 100 mL of 0.06 mL/l malathion solution (Malathion purity >95% from Nasr Company for Intermediate chemicals, Egypt) and was kept in dark for 6 hours to allow the system to reach an adsorption desorption equilibrium. Adsorption kinetics experiments were operated in a series of 250 mL beakers containing AgX NP’s and 100 mL of malathion solutions with continuous stirring at 25˚C under the UV illumination using a 250 W xenon arc lamp (Thoshiba, SHLS-002) (λ = 365 nm). After recovering the catalyst by centrifugation, the process was followed up by scanning the UV-Vis spectra at different time intervals within the wavelength range 220 - 350 nm and the band of maximum absorbance at 270 nm (λ_max for Malathion) was taken to follow up the degradation process.

The as-prepared AgX NP’s were firstly subjected to extensive study to confirm their chemical structure. Different techniques were performed for this purpose:

The antimicrobial susceptibilities against two Gram-positive bacteria and four Gram-negative bacteria in addition to five fungi were tested by the disk diffusion technique. Standard drug; tetracycline (500 µg∙ml⁻¹) and dimethyformamide (DMF) were screened separately for their antibacterial activity as positive and negative controls, respectively, while Nystatin (1000 Unit∙ml⁻¹) and DMF were screened separately for their antifungal activity as positive and negative controls, respectively The antibacterial and antifungal results (c.f. Table 5 and Table 6) suggest that the prepared AgXNP’s show high activity against the tested organisms compared to tetracycline and Nystatin taken as standard drugs.

*Dimethylformamide (DMF); **Tetracycline (500 µg∙mL⁻¹).

*DMF; **Nystatin (1000 Unit∙ml⁻¹).

The most acceptable mechanism for the antimicrobial effect of the nano materials is the in-situ production of reactive oxygen species (ROS) which occurs by the metal surface reducing oxygen molecules [29] . The species produced in these reactions are the hydroxyl radical (∙OH), superoxide ( O 2 − ), singlet oxygen (O₂) and hydrogen peroxide (H₂O₂). If the amount of ROS produced within the cell by metal nanoparticles increases too much the cell will not be able to survive the damage. This leads to the reduction of the activity of periplasmic enzymes which are needed for the health of the bacteria [29] . Silver nanoparticles have been shown to react with water to produce hydroxyl radicals and react with oxygen to produce superoxide and singlet oxygen [30] .

Among the organophosphorus insecticides, malathion is the most widely used (32% - 44% of total organophosphorus insecticide) [31] . Malathion [S-(1,2-dicarbethoxyethyl)-O,O-dimethyldithiophosphate], is a non-systemic, wide-spectrum organo-phosphorus pesticide used in public health, residential, and agricultural settings. It is classified as a toxicity class III according to Environment Protection Agency (EPA) [32] and can be degraded chemically and microbiologically in water within a few weeks, but it can remain in the environment for months [33] .

The photodegradation of Malathion as VX chemical warfare agent (CWA) stimulant and as widely used insecticide was studied without using catalyst and with using AgCl and AgBr NP’s as catalysts. The results are represented, graphically in Figure 7 and Figure 8. Inspection of the absorption spectra and the calculated % degradation values shows that, after 240 min Malathion degraded maximally up to 48.5% under the effect of UV radiation only, while the percent degradation efficiencies reach 99.2% and 82.4% on using AgCl and AgBr nanoparticles, respectively as catalyst within only 120 min. This reflects the high efficiency of these materials for the removal of such toxic organic insecticide pollutant.

Studies on the effect of pH on the % removal of malathion were studied keeping the mass of catalysts constant (0.1 g) and measuring the absorbance at 265 nm after 150 min constant stirring where it was found that (c.f. Figure 9) best removal takes place at, more or less, neutral solution (pH = 6.5 - 8.0).

The photocatalytic mechanism of Ag/AgX nanocomposites is displayed in Figure 10, [4] . When photons are absorbed, AgX produces an electron and a hole. This causes an electron transfer and, subsequently Ag⁺ transforms into Ag⁰ so forming Ag/AgX NP acting as photocatalyst. The Ag metal as a conductor grown on the surface of AgX can easily generate electron-hole pairs, then those electrons in the valance band can absorb photons with energy equal to or higher than the band gap energy. The main process that can generate reactive oxygen species (ROS) is the photo-generated charge-mediate redox reactions, which include the oxidation of H₂O to form OH^∙ radicals, and the reduction of O₂ to form (ROS) (e.g., singlet oxygen, hydroxyl radical, superoxide, hydroperoxyl radical, and hydrogen peroxide) [34] [35] .