**4.2 Chemical methods**

*Silver Micro-Nanoparticles - Properties, Synthesis, Characterization, and Applications*

without being overpriced [28, 29].

**4. Approaches for obtaining NPs**

its break down into nanostructures.

appropriate size and shape is gathered [32].

method consists of mechanisms like [30]:

with an absolute accuracy [35].

(**Figure 4**):

explained below:

**4.1 Physical methods**

electrodes [33].

So, sprayers originated from nanotechnology discharging airborne particles & Ag compounds have proven to boost good human health. Such ways substantiate a better air quality in communal places & provides enhanced protection against COVID-19 at its primary stage. Thus, mobile oxygen generating system & air coolers can easily be equipped with Ag NPs coated filters with improved efficiency &

Many convincing procedures have been awarded for processing Ag NPs in the past years [30]. NP production is briefed under two elemental categories

*Bottom-up Approach*: - Its initiates from atomic scale & generates NPs, until

Physical, Chemical, & Biological Methods to process the Ag NPs are

*Top-down Approach*: - Solid bulk material is applied with external force, forcing

These could be defined as the green mechanism because of non-synthetic liquids

in the tidy, thin films. Moreover, high consistency of NP distribution, is one of the pros of physically processed NPs as identify with any other methods [22]. This

• *Arc Discharge* - Condensation, nucleation, & construction of NPs pursues when marked component is volatilized via an arc discharge between

ablation, magnetron plasma sputtering, and many other [34].

• *High-Pressure Magneton Sputtering* - It falls under bottom-up process & inhabits in abridgment of super-saturated vapor via cold inert gas flow. This vapor atmosphere is acquired by discrete processes like thermal evaporation, laser

• *Laser Ablation* – A laser beam radiates to separate top layers of the bulk material

*Representation of two elemental categories, 'top-down' & 'bottom-up' approaches for the nanoscale material* 

**112**

**Figure 4.**

*processing [31].*

A chemistry professor from Princeton - John Turkevich's work in the 1950s, gave a highlight to chemical methods. The chemical processing by natural and artificial reducing surfactants is the preferred method for constructing Ag NPs. Reducing agents like sodium citrate, ascorbate, elemental hydrogen, are generally employed for Ag+ ions reduction in aqueous or non-aqueous solution. These agents shrink Ag+ ions forming Ag0 [36]. Protective agents are obligatory to stabilize breaking-up of NPs during their preparation and to restrict them to stay onto material surfaces [37]. To stabilize particle hike and to sustain them from sedimentation, accumulation, or losing surface properties, comprising functionalities to unite with molecule skin, the presence of surface-active agents like acids, amines, or alcohol are must [22]. This method comprises of [30, 38]:


## **4.3 Biological methods**

These are categorized under green synthesis and comprises polysaccharides, organic & irradiation techniques, preferred over other traditional practices requiring synthetic agents with hefty harms [43]. Because of benefits like organic surfactants (bacteria, fungi, yeast, and plant), cheap and eco-friendly techniques, a vast interest is gained by these methods. Even with natural surfactants, it has a usual reduction process [30]. Green synthesis pursues with:

