Modification of Spirulina sp. algae by exchanging Na+ cations and hexadechyltrimethylammonium+ (HDMTA)+ for removal of methyl orange and crystal violet dyes from solution

Spirulina sp. (AlgS) was modified with the cationic surfactant hexadechyltrimethylammonium bromide (HDTMA-Br) to produce a positively charged adsorbent (AlgS-HDTMA) through a cation exchange reaction. The functional groups contained in the adsorbent were studied using an infrared (IR) spectrometer, while the surface morphology and constituent elements were studied using SEM-EDX. The AlgS-HDTMA adsorbent was applied to the mono-component and bi-component adsorption of methyl orange (MO) and crystal violet (CV) dyes. The adsorption experiments were carried out using the batch method to determine the kinetics, isotherms, mechanisms, and adsorption competition of MO and CV against the adsorbent. The amount of MO and CV adsorbed by AlgS-HDTMA was compared with the adsorbent modified by Spirulina sp. algae with Na+ ions (AlgS-Na) in the form of both mono-component and bi-component which showed greater results than AlgS-Na. MO and CV adsorption competition against AlgS-HDTMA was dominated by MO with the bi-component Langmuir isotherm constant (bj) for MO and CV of 15.60 and 2.80 × 10–2 L/mmolequiv, respectively. Surface modification of AlgS with cationic surfactant HDTMA-Br has resulted in a rich positive charge, making it more effective to adsorb anionic dyes such as MO. Data on the ability to reuse adsorbents are an important aspect in handling wastewater treatment because it is very meaningful in reducing water treatment costs. The results of adsorption of MO solution and desorption with 0.1 M hydrochloric acid solution as eluent with 1–4 repetitions were: 97.8, 94.13, 89.39, and 86.27%. These data indicate that the repetition of 4 times did not significantly reduce the adsorption capacity of MO. Lastly, the wastewater study confirms that AlgS-HDTMA adsorbents are promising as biomass for anionic/cationic dye adsorption. The review is highly beneficial for scientists, wastewater treatment, and industrial communities to support the sustainable development of natural resources.