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Abstract: This review aimed to investigate the effect of pH on morphology, and size of gold nanoparticles (AuNPs) biosynthesized using extracts of various plant parts and agricultural waste. By reviewing previous studies, it was found that the formation of AuNPs was more rapid in neutral and basic mediums than in acidic mediums. Furthermore, most of those studies indicated that the smallest sizes of biosynthesized AuNPs, produced by plant extracts, were in neutral and alkaline mediums. Regarding the morphology, it was found that multiple shapes of the AuNPs were obtained in an acidic medium of the reaction, while there was typically a dominant shape of the AuNPs in the basic medium. In conclusion, significant quantities of AuNPs with appropriate sizes and morphology could be obtained by controlling the medium of the reaction when AuNPs are biosynthesized using extracts of plant parts and agricultural waste.

Biosynthesis techniques have a number of advantages over other methods for producing silver nanoparticles (AgNPs), which provide a wide range of applications. The present work highlights the biosynthesis of AgNPs by mixing pear leaf aqueous extract with silver nitrate, and the formation of AgNPs was observed by the change of mixture color from yellow to dark brown and visible spectrophotometry. Moreover, the effect of pH, reaction time, AgNO3 concentration, extract volume and temperature on the suggested approach was also studied. The results showed that pear leaf aqueous extract is an excellent material for the biosynthesis of AgNPs, and by controlling the mentioned parameters that influence synthesis, a large number of AgNPs with small sizes may be produced. Keywords: silver nitrate, silver nanoparticles, pear leaves, biosynthesis 

Biosynthesis of the metallic nanoparticle is gaining importance because it’s a single-step process, nontoxic, environmentally acceptable, and easily scaled up. The present study investigated the biosynthesis of silver nanoparticles (AgNPs) via reacting olive wastewater filtrate (OWF) with silver nitrate, and the formation of AgNPs was confirmed by a color change of the reaction mixture and visible spectrophotometry. Additionally, the influence of pH, reaction time, AgNO₃ concentration, temperature, and OWF volume on the proposed method was investigated. It was found that with increasing the previously mentioned parameters, the formation of the AgNPs was increased under the experimental conditions. The results showed that OWF represented a promising material for the biosynthesis of AgNPs.      

Abstract:

This study investigated the potential use of olive pomace (OP) as an adsorbent to

reduce the concentration of methyl orange (MO) in aqueous solutions. The effect of

some important parameters on the process of adsorption was examined, including

pH, adsorbent weight, temperature, contact time, agitation speed, and the initial

concentration of MO. The results showed that the optimum concentration of MO was

10 ppm and the optimum pH = 2, indicating that the process of MO adsorption on the

surface of the OP was better in acidic medium. The equilibrium time was 80 min at a

speed of 100 rpm. The results of the study showed the significant role of OP weight,

agitation speed, temperature and the contact time in increasing the adsorption

efficiency. On comparing the pseudo first order and pseudo second order models, the

results showed that the pseudo second order model fitted the experimental data well.

The study also included testing of Langmuir and Freundlich models on the

adsorption isotherm data, and it was found that experimental data obey the

Freundlich isotherm. To sum up, the study showed that OP has high adsorption

efficiency to remove MO by applying a simple, inexpensive method.