Organic dye removal and recycling performances of graphene oxide-coated biopolymer sponge

In this study, a biopolymer sponge (PS) with a cross-linked mixture of gelatin-chitosan-poly(vinyl alcohol) was dipped into graphene oxide (GO) solution to form a composite sponge (CS, GO-coated PS) by a combination of simple dip-coating and freeze-drying procedures, as a sponge-like adsorbent in organic dye removal applications. The morphological, chemical, crystalline, mechanical and thermal characterizations of the as-obtained sponges were further investigated for the possible changes in the structure of sponge-like adsorbent after coating the GO sheets on the 3D porous structure of PS. The results showed that the CS had possessed effectively organic dye removal performances comparing to the PS. In the adsorption, the Langmuir and pseudo-second-order models corresponding to a monolayer approach and a chemical adsorption were appropriated. The maximum adsorption capacity of Rhodamine B and Congo red reached 126.8 and 135.0 mg-g(-1); and 145.6 and 148.6 mg-g(-1) corresponding onto the PS and CS. It indicates that the maximum adsorption capacity on the CS enhanced significantly comparing to those on the PS owing to the functional GO sheets coated in the 3D porous structure of PS, which leads to supplying further functional adsorption sides on the whole 3D porous structure of CS. Notably, the sponges-like adsorbents could be regenerated and used again without a remarkable decrease of dye removal ability occurred in 9 adsorbing-desorbing cycles. Therefore, the CS prepared in this study can become a potential adsorbent for actual applications because of non-toxic materials, proper structural features, low-cost material and operation, and reliable recyclability.

Automated summary

In this study, a composite sponge was developed by coating a biopolymer sponge with graphene oxide, which showed improved adsorption performance for organic dyes. The coated sponge had a higher maximum adsorption capacity compared to the uncoated sponge, and it could be regenerated and reused without significant loss of dye removal ability. This study provides a potential adsorbent with non-toxic materials and reliable recyclability.