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A green monolithic starch cryogel was prepared and applied for the removal of methylene blue (MB) using a batch system. The influence of various experimental parameters on MB adsorption was investigated. High removal efficiency (81.58 ± 0.59%) and adsorption capacity (34.84 mg g−1) were achieved. The Langmuir model better fitted the experimental data (determination coefficient (R2) = 0.9838) than the Freundlich one (R2 = 0.8542), while the kinetics of MB adsorption on the cryogel followed a pseudo-second-order model. The adsorption process was spontaneous and endothermic with an activation energy of 37.8 kJ mol−1 that indicated physical adsorption. The starch cryogel was used for MB removal from a wastewater sample collected from a local Batik production community enterprise in Phuket, Thailand, and a removal efficiency of 75.6% was achieved, indicating that it has a high potential as a green adsorbent for MB removal.

Monolithic cryogels from starch were successfully synthesized and applied as alternative biodegradable filters for the first time. Rice flour was cross-linked with Ca2+ from limewater during gelatinization before being frozen and then thawed for three cycles. The resultant material was then soaked in ethanol for 3 h before incubation at 80 °C for 1 h, yielding monolithic material with interconnected pores in sizes of 51 ± 18 to 52 ± 15 µm without any need of freeze-drying. The cryogels possessed macroporous structure with specific surface areas from 1.1 to 4.3 m2g−1, they could adsorb water from 599 ± 27 to 635 ± 59% of their dry weight with low swelling ratios of 6.0 ± 0.3 to 6.4 ± 0.6 gwater/gcryogel, and could be applied as biofilters to remove suspended particles and reduce the light absorption of water sample from 25 ± 3 to 96 ± 5%. The prepared biofilters can be re-used up to three times, although they cost only USD 0.0004/piece. Complete weight loss resulted from burial in soil for 30 days, indicating environmentally friendly biodegradation and potential for environmental applications.

This work presents a novel, simple, rapid, and cost effective method for semi-quantitative analysis of arsenic (III) in water sample. The method was based on the digital image colorimetry (DIC) of difluoroboron-curcumin doped starch film (BF 2-cur-film) and arsenic ion in water. A red BF 2-cur-film (9.4 m) was fabricated by entrapped difluoroboron-curcumin (BF 2-curcumin, particle size of 60-113 nm) in tapioca starch film. When the standard solution of arsenic (1 mL) was added into small plastic tube containing BF 2-cur-film on its inner lid, blue solution ( max at 610 nm) was observed instead of orange color in blank solution ( max at 495 nm). When BF 2-cur-film was used in conjunction with DIC, a wide linear range of 0-10 mgL-1 with good linearity (R 2 > 0.99) was obtained from green channel with low detection limit of 0.04 mgL-1. Moreover, good precision (0.9-1.2%RSD, n = 4 days) and accuracy (0.03% relative error) were also achieved.

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