Adsorptive removal of hazardous rhodamine B dye from aqueous solutions by St. John’s wort (Hypericum perforatum)
Birol Işık
Abstract
Abstract In this work, it was aimed to remove the highly toxic rhodamine B (RhB) dye from wastewater by using a low-cost, renewable, sustainable, and completely natural adsorbent obtained from St. John’s wort ( Hypericum perforatum ) (HP), which is considered an agro-waste. HP was characterized by FTIR-ATR, XRD, FESEM, and pH pzc . Adsorption experiments were conducted by optimizing pH (2–12), dose (0.01–0.30 g), time (0–120 min), and concentration (10–50 mg/L). Equilibrium data were applied to linear isotherms. The results stated that the removal process occurred in a monolayer on the homogeneous surface of HP and the $${q}_{m}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>q</mml:mi> <mml:mi>m</mml:mi> </mml:msub> </mml:math> value was determined as 196.08 mg/g at 298 K. Kinetic results showed that RhB adsorption on HP followed a quasi-second-order. The effect of salt concentration onto RhB adsorption on HP adsorbent and reusability studies were conducted. Thermodynamic tests showed that the process was exothermic ( $${\varDelta H}_{A}^{o}=-13.58 kJ/mol$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msubsup> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:mi>H</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>A</mml:mi> </mml:mrow> <mml:mi>o</mml:mi> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mo>-</mml:mo> <mml:mn>13.58</mml:mn> <mml:mi>k</mml:mi> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>m</mml:mi> <mml:mi>o</mml:mi> <mml:mi>l</mml:mi> </mml:mrow> </mml:math> ) and spontaneous ( $${\varDelta G}_{A}^{o}=-26.61 kJ/mol$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msubsup> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:mi>G</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>A</mml:mi> </mml:mrow> <mml:mi>o</mml:mi> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mo>-</mml:mo> <mml:mn>26.61</mml:mn> <mml:mi>k</mml:mi> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>m</mml:mi> <mml:mi>o</mml:mi> <mml:mi>l</mml:mi> </mml:mrow> </mml:math> ). The results of the study indicated that HP may be a favorable adsorbent for basic dyes in wastewater. Graphical abstract