Silver nanoparticles (AgNPs) are intensively investigated for their superior physical, chemical, and biological properties. A proper knowledge of these properties is essential to maximizing the potential applications of AgNPs in several areas while minimizing their risks to humans and the environment. This paper aims to critically review AgNPs from the perspectives of research trends, global consumption, synthesis, properties, and future challenges. Generally, AgNPs can be synthesized using three methods, namely physical, chemical, and biological, and the related works as well as their numerous advantages and disadvantages are presented in this review. In addition, AgNPs can be potentially explored for various applications. Future challenges on (AgNP) synthesis, their release into the environment, and scaling up production, as presented in the review, suggest that several potential topics for future works are available to promote a safer and more efficient use of these nanoparticles. Studies on AgNPs in Malaysia have increased since the Malaysian government officially established a directorate for nanotechnology development. This calls for a proper set of policies on AgNPs starting from their production to utilization as well as their effects on various related industries and the environment.

The ubiquitous problem of pesticide in aquatic environment are receiving worldwide concern as pesticide tends to accumulate in the body of the aquatic organism and sediment soil, posing health risks to the human. Many pesticide formulations had introduced due to the rapid growth in the global pesticide market result from the wide use of pesticides in agricultural and non-agricultural sectors. The occurrence of pesticides in the water body is derived by the runoff from the agricultural field and industrial wastewater. Soluble pesticides were carried away by water molecules especially during the precipitation event by percolating downward into the soil layers and eventually reach surface waters and groundwater. Consequently, it degrades water quality and reduces the supply of clean water for potable water. Long-time exposure to the low concentration of pesticides had resulted in non-carcinogenic health risks. The conventional method of pesticide treatment processes encompasses coagulation-flocculation, adsorption, filtration and sedimentation, which rely on the phase transfer of pollutants. Those methods are often incurred with a relatively high operational cost and may cause secondary pollution such as sludge formation. Advanced oxidation processes (AOPs) are recognized as clean technologies for the treatment of water containing recalcitrant and bio-refractory pollutants such as pesticides. It has been adopted as recent water purification technology because of the thermodynamic viability and broad spectrum of applicability. This work provides a comprehensive review for occurrence of pesticide in the drinking water and its possible treatment.

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The current status of silver nanoparticles (AgNPs) in the water environment in Malaysia was examined and reported. For inspection, two rivers and two sewage treatment plants (STPs) were selected. Two activated carbons derived from oil palm (ACfOPS) and coconut (ACfCS) shells were proposed as the adsorbent to remove AgNPs. It was found that the concentrations of AgNPs in the rivers and STPs are in the ranges of 0.13 to 10.16 mg L−1 and 0.13 to 20.02 mg L−1, respectively, with the highest concentration measured in July. ACfOPS and ACfCS removed up to 99.6 and 99.9% of AgNPs, respectively, from the water. The interaction mechanism between AgNPs and the activated carbon surface employed in this work was mainly the electrostatic force interaction via binding Ag+ with O− presented in the activated carbon to form AgO. Fifteen kinetic models were compared statistically to describe the removal of AgNPs. It was found that the experimental adsorption data can be best described using the mixed 1,2-order model. Therefore, this model has the potential to be a candidate for a general model to describe AgNPs adsorption using numerous materials, its validation of which has been confirmed with other material data from previous works.

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The growth of white-rot fungus Pleurotus eryngii F032 in a suitable medium can degrade an azo dye Reactive Black 5 (RB5), because of its ability to produce ligninolytic enzymes such as lignin peroxidase (LiP), manganese peroxidase (MnP), and laccase that able to degrade and transform the complex structure of the dye into a less toxic compound. The effect of environmental factors such as initial concentration of Reactive Black 5, pH, temperature of growth medium, surfactant (Tween 80), and agitation were also investigated. The productions of ligninolytic enzymes were enhanced by increasing the white-rot fungi growth in optimum conditions. The decolorization of Reactive Black 5 were analyzed by using UV-vis spectrophotometer at the maximum absorbance of 596 nm. The whiterot fungus, P. eryngii F032 culture exhibited 93.56 % decolorization of 10 mg/L RB5 within 72 h of incubation in dark condition with agitation. The optimum pH and temperature for the decolorizing activity was recorded at pH 3 and 40°C, respectively. The addition of surfactant (Tween 80) increased the decolorization to 93.57 % and agitation of growth medium at 120 rpm enhanced the distribution of nutrients to the fungus thus optimized the enzymatic reaction that resulted maximum decolorization of RB5 which was 93.57 %. The molecular docking studies were performed using Chimera visualization software as to analyze the decolorization mechanism of RB5 at molecular level.

Utilization of microbes including white-rot fungi and bacterial strains for decolorization of synthetic dyes is one promising strategy of an environmentally friendly and cost-competitive alternative to physicochemical decomposition processes for treating industrial effluents. In this study, the biodegradation ability of the white-rot fungi Polyporus sp. S133 that produce high laccase was investigated in order to decolorize anthraquinone-type dye. Parameter including pH, temperature, and non-ionic surfactant were used to comparatively study the decolorizing effects on Remazol Brilliant Blue R (RBBR). The purified laccase totally decolorized 200 mg L −1 initial concentration of RBBR dye when only 1.5 UL −1 of laccase was used in the reaction mixture. The optimal decolorization rates were achieved at pH 5 and at a temperature of 50°C. N-hydroxybenzotriazole, a small molecular weight redox mediator, was found to accelerate the decolorization. Tween 20 inhibited the decolorization while Tween 80 and Brij 35 showed no inhibition effect. Two compounds were identified as the intermediates (m/z 304.3 and m/z 342.2). These results suggest that laccase from Polyporus sp. S133 is a powerful tool for the decolorization of anthraquinone dyes. A pathway for the metabolism of the RBBR by laccase of Polyporus sp S133 was proposed. These proposed pathways could contribute to a better comprehension of the mechanisms used by oxidative enzymes to transform organic compounds.

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