Abstract
This study investigates the efficacy of acid activated coconut husk (CHA) for the removal of rhodamine-B (Rh-B) dye from aqueous solutions. The CHA prepared was characterized using various techniques: SEM, FTIR EDX, Boehm titration and pHpzc, respectively. The effects of different operational parameters including initial concentration, contact time and solution temperatures were examined. Kinetic data for Rh-B dye adsorption onto CHA fitted best to pseudo-second-order kinetic model considering the correlation regression (R2) and the sum of squares of error values. Adsorption data were fitted to Langmuir, Freundlich, Dubinin–Radushkevich and Temkin isotherm models. Langmuir isotherm was the most fitted among all the models used with maximum monolayer sorption capacity of 1666.67 mg g−1 and the highest regression value of 0.99 indicating that CHA has greater affinity for Rh-B dye adsorption due to increased pore development via acid activation. Thermodynamic studies revealed an endothermic adsorption process with the ΔH0 value of 62.77 kJ mol−1. Spontaneity was ascertained based on the negative values of ΔGo (ranging from − 26.38 kJ mol−1 to − 20.93 kJ mol−1). The positive value of ΔS0 (0.276 kJ mol−1 K−1) suggests increased randomness that exists between CHA and Rh-B dye. Cost analysis results revealed that CHA is six times cheaper than commercial activated carbon (CAC), providing a savings of 217 US$ kg−1. CHA adsorbent was found to be suitable for Rh-B dye removal from aqueous solution.
Highlights
Two-thirds of the Earth form the hydrosphere, the availability of fresh and quality water decreases as urbanization is globally encouraged
The need for suitable replacements opens an opportunity for the effective use of agricultural wastes as adsorbent, and some of these largely available and inexpensive adsorbents have been reported for dye removal including cocoa pod husk (Olakunle et al 2018) Moringa oleifera seed pod (Bello et al 2017b), scrap tires (Li et al 2010) Raphia hookerie fruit epicarp (Inyinbor et al 2016), rambutan seed (Ahmad et al 2016), Durian seed (Ahmad et al 2015), sugarcane bagasse (Saad et al 2010), bengal gram seed husk (Somasekhara Reddy et al 2017), walnut shell (Ojo et al 2019) among others
We have previously reported that only the samples that are richer in carbon and lower in oxygen contents proved to be efficient adsorbents for removing dyes and other pollutants from the aqueous solutions (Bello et al 2017a)
Summary
Two-thirds of the Earth form the hydrosphere, the availability of fresh and quality water decreases as urbanization is globally encouraged. Among different conventional methods used for water treatment, adsorption process by activated carbon (AC) remains one of the sustainable approach to removing various pollutants (Deschaux et al 2011; Adegoke and Bello 2015; Bello et al 2015) This method is not complex for an average skilled technician to master and requires only limited resources; industries can adopt this noble method (Kooh et al 2016). Commercial activated carbon (CAC), used conventionally for adsorption processes and other varieties of application, is scare, expensive and non-renewable (Namasivayam and Sangeetha 2006; Parab et al 2009; Gupta et al 2010; Khan et al 2011; Wang and Chu 2011; Jain et al 2015; Rani et al 2017). The need for suitable replacements opens an opportunity for the effective use of agricultural wastes as adsorbent, and some of these largely available and inexpensive adsorbents have been reported for dye removal including cocoa pod husk (Olakunle et al 2018) Moringa oleifera seed pod (Bello et al 2017b), scrap tires (Li et al 2010) Raphia hookerie fruit epicarp (Inyinbor et al 2016), rambutan seed (Ahmad et al 2016), Durian seed (Ahmad et al 2015), sugarcane bagasse (Saad et al 2010), bengal gram seed husk (Somasekhara Reddy et al 2017), walnut shell (Ojo et al 2019) among others
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