Preface

One of the most recent trends in environmental technology is the research turn to green chemistry. It is generally accepted that one of the most promising techniques for wastewaters treatment is adsorption. On this basis, numerous adsorbent materials have been synthesized up to now. However, nowadays, there is a novel concept, which promotes the use of materials with the lowest possible cost. The economic crisis of the 2000s led researchers to turn their interest to adsorbent materials with lower cost. Attempts were already realized to use some low-cost adsorbent materials in order to initially treat synthetic aqueous solutions and then real industrial samples. In this eBook, the main scope is to describe these environmental-friendly materials namely “green adsorbents”, as I firstly introduce this term. With this term, it is meant the adsorption process using low-cost materials originated from: (i) agricultural sources and by-products (fruits, vegetables, foods); (ii) agricultural residues and wastes; (iii) low-cost sources from which most complex adsorbents will be produced (i.e., activated carbons after pyrolysis of agricultural sources).

It is a fact that low-cost adsorbent materials belong to a hot-topic of recent literature given its economic perspective. Although they present a slightly lower adsorption capacity compared to more complex materials (i.e. polymers), their near zero cost of preparation makes them very attractive in chemical technology. In this field, some crucial factors will be developed regarding the removal of those environmental pollutants from aqueous systems with the aforementioned type of materials.

Three main categories of environmental pollutants are discussed as: (i) dyes; (ii) heavy metals, and (iii) others (phenols, pesticides/insecticides etc). This category will be preferred to be presented as general category of “others”, because the number of published works for this type of pollutants is still limited compared to those of dyes or metals.

Extensive comparison will be done for: (i) their adsorption capacity, showing the main models used up to now for the expression of their theoretical maximum capacity theoretically; (ii) their kinetic behavior, showing the main models used and some more specific kinetic simulations; (iii) parameters influenced by adsorption (salinity, particle size or mass of adsorbent etc); (iii) their reuse potential, given the ultimate goal of each adsorbent to be used in industrial/factorial design; (iv) fixed-bed columns; (v) the surface of those low-cost materials (comments about their characterization); (vi) economic perspectives; (vii) future trends and applicability.