**3. Multifunctional aspects of phytomass-derived activated carbon**

It can thus be seen that due to the increasing demand of AC, there is a strong need for the sorting out of new precursors for AC which should be cost effective than the commercially available ACs. Although, a variety of raw materials were explored for the preparation of AC in earlier studies, scientists are still exploring new materials depending on their availability and suitability for producing AC with multi-functions. Additionally, application of phytomass carbon electrodes stands as an important class of technology where 3R principles are followed. Thus remarkably, the utilization of phytomass as raw material for the preparation of AC has increased in recent years in view of the foregoing facts on AC. In the following sections, interesting multifunctional aspects of phytomass-derived AC will be deliberated.

#### **3.1 Application of phytomass-derived AC as an adsorbent**

The use of charcoal or AC for the adsorption (removal) of pollutants in air or toxic ions and dyes from contaminated water is best known for over 80 years and further adsorption properties, mechanisms, kinetics and theories of adsorption are also well established. But the potential of economically cheaper and renewable phytomass-derived AC as adsorbent was understood since the past decade though the search for better AC is still going-on due to the exponential demand for treatment of industrial effluents.

There are enormous sorptive studies with biomass-derived activated carbons and to cite a few; Tura and Tesema [32] have removed methylene blue using AC derived from *Delonix regia* seed pods. They have shown that adsorption of methylene blue is mainly pH dependent and that maximum adsorption takes place in slight neutral pH. Electrical conductivity and total suspended solid was found to decrease after adsorption which, indicates the decrease of ions from methylene blue dye proving the removal of color i.e. the dye. In yet another special work, Sekaran et al. [33] have reported the preparation of mesoporous-activated carbon from rice husk by precarbonization at 400°C, chemical activation using phosphoric acid at various temperatures and have immobilized Bacillus sp. in the mesoporousactivated carbon for the degradation of sulphonated phenolic compounds in

wastewater. *Delonix regia* derived AC has also been utilized to remove Hg [34], Pb and Ni [35].

Good amount of work has been reported on fluoride removal from water. Fito et al. [36] have done a very significant work using H2SO4 activated *C. edulis* stem derived AC for the removal of F from aqueous solutions. Stem of the *Vitex negundo* plant [37], CaCl2-modifed *Crocus sativus* leaves [38] and bark of *Morinda tinctoria* [39] are further interesting works involving F removal. **Figure 5** is a picture where adsorbed molecules in the pores of the AC are shown.

Above reports are just bits from a massive published literature. However, readers can have a detailed outlook from Jorge Bedia et als' report [41] where they have made an excellent exhaustive review on the synthesis and characterization of biomass-derived carbons for adsorption of emerging contaminants from water. All the above read reports convey the need for commercially viable and potential activated carbon-based adsorbents.

## **3.2 Application of phytomass-derived AC for preparing electrocatalyst for hydrogen gas from water electrolysis**

It is well known that, noble metals like Pt and Ru based electrocatalysts are employed for producing hydrogen by electrolyzing water and usually electrocatalysts are fabricated by supporting or loading fine Pt or Ru particles on quality carbon powders (the carbon is called catalyst support), such that more number of active sites will be available for efficient and complete electrolysis. Falling in that line, an innovative and ever first attempt has been reported by the authors of the present chapter on adopting a zero-cost green precursor viz., grass biomass, by converting the grass biomass into a biochar and attempting to produce an electrocatalyst with platinum for generating hydrogen gas through electrolysis of water [42].

Cleaned turf grass blades were chosen as the phytomass of producing AC for supporting Pt particles to finally utilize as electrocatalyst for hydrogen gas generation through electrolysis of water. The procedure involved an activation of grass blades with ZnCl2 followed by heat treatment at 250°C. As an initial trial, 1% Pt was supported over the grass-derived AC powder to result in Pt@G-AC. After various physical characterization studies, Pt@G-AC powder was assessed for catalytic activity in 1 M sulphuric acid solution for H2 generation through linear sweep and cyclic voltammetric studies. Encouraging results were obtained suggesting that grass can be considered as a renewable alternative for producing carbon supports

for electrocatalysts but also paves way for the production of low-cost carbon for other applications like adsorbent for color, odor and hazardous pollutants and electrode materials as well, as will be highlighted in the subsequent sections. **Figure 6** gives LSV plot of G-AC with and without 1% Pt electrodes in 1 M H2SO4. Since no other reports are available on this particular application it seems that intensive research is this area is highly required and hence it is expected to pick up in the future.
