The manganese spinel ferrite (MnFe 2 O 4 ) particles were successfully synthesized via a hydrothermal route in green betel leaf (Piper betle Linn) extract media. Morphology, structure, and characteristics of the samples were analyzed by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), X-Ray Diffraction (XRD), Fourier-Transform Infrared (FT-IR), Diffuse Reflectance Spectroscopy UV-Vis (DRS UV-Vis), and Vibration Sample Magnetometer (VSM) instruments. Photocatalytic activity of the spinel ferrite was evaluated by the degradation of dye under solar light and antibacterial activity was studied with different strains of Gram-positive and Gram-negative bacteria. The results revealed that the concentration of betel leaf extract was an important factor, which affects the morphology, crystallization, and magnetic properties of MnFe 2 O 4 . The prepared samples exhibited soft-ferromagnetic behavior at room temperature. Un-calcined samples showed higher saturation magnetic ($65 emu/g) than calcined samples (29-41 emu/g). The band gap energy of synthesized samples was about 2.05 eV. Two major wide-ranging metal-oxygen (M-O) peaks are seen in the FT-IR spectra in the range of 570-300 cm À1 , which confirmed the presence of tetrahedral and octahedral sites in the spinel structure. The MnFe 2 O 4 particles showed effective photodegradation for Direct Red 81 dye under solar light irradiation. Moreover, the prepared samples exhibited significant activity as an antibacterial against Staphylococcus aureus and Escherichia coli.

In this work, the semiconductor of ZnO-CoFe2O4 composites were prepared by green synthesis approach using rambutan peel extract (Nephelium lappaceum L.) as a capping agent. X-ray diffraction patterns of composites showed the main peaks of ZnO at 2θ = 31.8°, 34.5°, and 36.2° corresponding to hexagonal wurtzite structure and weak peak at 2θ = 35.4° for cubic structure of CoFe2O4. The formation of rice-like and small granular morphology were confirmed by scanning electron microscope (SEM) and transmission electron microscope (TEM), whereas the superparamagnetic behavior of the samples were determined by vibrating sample magnetometer (VSM). The spectrum of Fourier transform infrared (FTIR) and x-ray photoelectron spectroscopy (XPS) showed absorption bands related to a number of interactions and binding energy in the samples respectively. The photocatalytic performance of composites under solar light was evaluated for the degradation of Direct Red 81 and the dye from washing water of batik garments. The composites showed good photocatalytic activity with the degradation percentage reaching 99.6% for Direct Red 81 dye after 2 hours.

Magnetic nanoparticles of TiO2-(x)NiFe2O4 with x = 0.01, 0.1, and 0.3have been synthesized by mixture of titanium isopropoxide (TIP) and nitric metal as precursors. The particles were characterized by XRD, SEM-EDX, and VSM. XRD pattern show the peaks at 2q = 25.3°, 38.4° and 47.9° which are referred as anatase phase of TiO2. Meanwhile NiFe2O4 phase was observed clearly for x = 0.3. The present of NiFe2O4 can prevent the transformation of TiO2 from anatase to rutile when the calcination temperature increased. Microstructure analyses by SEM show the homogeneous form and size of particles. The magnetic properties analysis by VSM indicates that TiO2-NiFe2O4 is paramagnetic behavior. TiO2 doped NiFe2O4 has higher photocatalytic activity than TiO2 synthesized for degradation of Rhodamine B in aqueous solution under solar light irradiation.

Mangifera odorata Griff seed extract as a corrosion inhibitor of mild steel in 1M hydrochloric acid solution was investigated by weight loss, potentiodynamic polarization, and scanning electron microscopy methods. The results showed that the extract was able to inhibit the corrosion of mild steel with an inhibition efficiency of more than 90% at 8 g/L Mangifera odorata Griff seed extract in 1M hydrochloric acid solution. The inhibition efficiency was found to be increased with increasing the extract concentration and decreased with increasing temperature. The adsorption of Mangifera odorata Griff seed extract on the mild steel surface follows the Langmuir adsorption isotherm and behaves as a mixed type inhibitor. The value of the highest inhibition efficiency of 91.78% was obtained by weight loss and 94.55% by potentiodynamic polarization method at MOSE concentration of 8 g/L and the immersion temperature of 30 o C. Thermodynamic parameter values from the adsorption process indicate that the extracts can function as inhibitors due to it can increase the activation energy of mild steel dissolution.

The corrosion of steel and its alloys is an important problem in industry, especially in acidic environments. Mild steel is one of the important alloys of iron which has many industrial applications because of its excellent mechanical properties, but mild steel is susceptible to corrosion. Corrosion problems need to be a concern and must be handled properly. Hydrochloric acid is widely used for pickling, cleansing, decomposition and metal etching, on the other hand also contributes to corrosion of metal surfaces. Plant extracts investigated the properties, mechanisms of adsorption and efficiency of inhibition as environmentally friendly corrosion inhibitors for various steel materials in different acidic media. The efficiency of corrosion inhibition of steel from plant extracts analyzed ranged from 72-98% and generally as a mixed-type inhibitor. Most of the inhibitors are adsorbed on the steel surface through a physisorption mechanism.