Superior selective adsorption of MgO with abundant oxygen vacancies to removal and recycle reactive dyes

In textile engineering, wasted mixture dyes are often discharged and need to be separated and recycled. To solve this problem, MgO with abundant oxygen vacancies (F+ centers, F+-MgO) is studied as a selective adsorbent for the recycling and separation of organic dyes. Herein, the adsorption performance of F+-MgO to reactive dyes Reactive blue 19, Reactive red 195, Congo red (RB19, RR195, CR), and non-reactive dyes Methylene blue and Rhodamine B (MB and RB), and the dyes mixture are estimated. Our results present that F+-MgO exhibits the properties of selective adsorption, separation, and recovery of reactive dyes from the dyes mixture. Equilibrium adsorption capacities (q(eth)) of F+-MgO are 549.45 mg/g to RB19, 348.43 mg/g to CR, and 442.48 mg/g to RR195, while hardly adsorption for MB and RhB, respectively. Moreover, RB19 can be quickly separated by F+-MgO from the mixture of RB19 and RhB in 90 s with an initial concentration of 50 mg/L. Furthermore, XPS, PL, and EPR confirm that the surface oxygen vacancies exist on the F+-MgO. And the surface oxygen vacancies are affirmed as adsorption active sites by reduced adsorption capacity after H2O2 treatment and heated at high temperature in O-2. The recycling of the used adsorbent F+-MgO is achieved by calcinated F+-MgO at high temperature, and the adsorption efficiency remains high (96.02%) after seven cycles. Notably, the adsorbed dyes (RB19) also can be reused by dissolution MgO into the solution. In this work, a low-cost, high-efficient, and recyclable adsorbent is applied to recover used-dyes from textile wastewater, presenting a new closed-loop sustainable strategy.