Application of Wasted Oolong Tea as a Biosorbent for the Adsorption of Methylene Blue

Abstract

Tea powder, a biosorbent prepared from wasted oolong tea, was collected as a prospective adsorbent for the adsorption of methylene blue (MB) from aqueous solution. e effect of factors on adsorption efficiency, isotherms, kinetics, and potential mechanism was carried out. Adsorption capacity of MB onto wasted tea powder increased with the MB concentration and contact time, whereas the increase in pH value and ion strength appeared to have a negative effect for the adsorption process. e adsorption efficiency increased rapidly and reached a stable state within 120 min. e optimal tea powder loading weight is suggested to be at 0.1 to 0.2 g, and the highest efficiency of 94.8% is achieved at 333 K. ere were no significant changes in adsorption efficiency when the effect of temperature is considered. e Langmuir isotherm model was found to be the best isotherm models to elucidate the adsorption mechanism in this study. e maximum adsorption capacities calculated at different temperatures by the Langmuir model ranging from 312.5 to 333.3 mg·g −1 were much close to the experimental results. From the kinetic analysis, the pseudo--second-order model was found to be the best model to describe the adsorption behavior. e calculated adsorption capacities at different initial MB concentrations by the pseudo-second-order model ranging from 92.34 to 400 mg·g −1 were well close to the experimental data. e fitting results obtained from the intraparticle diffusion model suggested that the intraparticle diffusion was not the only rate-controlling step and some other mechanisms along with the intraparticle diffusion were probably involved. e intraparticle diffusion of MB molecules into pore structures of wasted tea powder is the ratelimiting step for the adsorption process in this study. e repetitive cycle experiments indicated that the wasted oolong tea powder was efficiently regenerated using NaOH and thus be used for many times.

Greener Cleaner: Liquid-Phase Adsorption of Dye Using Macroalgae Based Biosorbent Materials

“…This is due to saturation of active sites on the adsorbent surface and exuthoin point takes place. This is agreement with several literatures that used low cost adsorbents for the removal of basic dyes from aqueous solution [16][17][18][19][20][21][22]. in trend with several works have been done previously by many researchers [16][17][18][19][20][21].…”

“…However, 0.25g was selected as optimum value of the adsorbent mass and has been used for the next stages. Similar trend for the influence of adsorbent amount on the adsorption efficiency for basic dyes was observed and reported in previous studies for other types of low-cost adsorbents[15][16][17][18][19][20][21][22][23].…”

“…The results show that the percentage removal of CV dye rapidly increased with increasing pH values until reaches maximum at pH (6.5). A similar behavior was observed for the removal of basic dye from aqueous solution by orange peel powder [16], coffee waste [18], wasted Oolong tea [19], Gmelina Arborea biomass [20], olive-waste cake [21], marine macroalgae [22].This trend may be described to electrostatic interaction between cationic dye (CV) and the negative surface of adsorbent. Lower removal of CV dye at the acid media may be due to the presence of excess H+ ions that complete with the basic dye for adsorption site [16].…”

Tea Stem as a Sorbent for Removal of Methylene Blue from Aqueous Phase

“…In addition, the heat of adsorption (b value) is 159.41 J/mol, which linearly decreases as MB molecules covered gradually tea stem powder. ese findings suggest that the electrostatic interaction is one of the important mechanisms between wasted tea powder and MB [52].…”

“…e Q cal values derived from pseudo-second-order are much close to the experimental values (Q exp ), demonstrating that the pseudo-second-order model is more appropriate for the prediction of kinetic process for MB adsorption onto tea stem powder. e idea fitting of the pseudo-second-order model means that the ratelimiting step is not the resistance of boundary layer and the adsorption of MB onto tea stem is a complicated process [52].…”