Continuous-Flow System for Methylene Blue Removal Using a Green and Cost-Effective Starch Single-Rod Column.

A continuous-flow system based on a green and cost-effective monolithic starch cryogel column was successfully developed for removing methylene blue (MB). The proposed column exhibited high removal efficiency (up to 99.9%) and adsorption capacity (25.4 mg·g-1) for synthetic and real samples with an adsorbent cost of USD 0.02. The influence of various operation parameters, including the flow rate, initial concentration, column height, and temperature, on the MB removal efficiency was examined and reported. The MB removal efficiency remained >99% in the presence of potential interferences, highlighting the good performance of the cryogel column. The Yoon-Nelson dynamic model explained the MB adsorption better than the Bohart-Adams model, as indicated by the higher R2 values (R2 = 0.9890-0.9999) exhibited by the former and current trends of its parameters. The MB removal efficiency of the cryogel column remained at 62.7% after three reuse cycles. The wastewater containing MB collected from a local batik-production community enterprise in Phuket, Thailand was applied to the proposed continuous-flow system under optimum conditions, and results indicated that 99.7% of the MB present in 2.4 L of wastewater was removed. These results validate the excellent application potential of the cryogel column for the continuous-flow adsorption of MB. This study will facilitate future industrial applications and process designs of the continuous-flow system.

Continuous Phosphate Removal and Recovery Using a Calcium Silicate Hydrate Composite Monolithic Cryogel Column.

Toward the development of a practical and green approach for removing phosphate from water, a monolithic cryogel based on starch and calcium silicate hydrate (Cry-CSH) was employed as a phosphate adsorbent in a continuous flow system for the first time. The influence of flow rate, initial phosphate concentration, and adsorbent height on the adsorption efficiency was investigated. As the rate of flow and the initial concentration of phosphate increased, the total quantity of adsorbed phosphate dropped; however, the performance of the column was greatly enhanced by an increase in adsorbent height. The experimental data fit the Adams-Bohart model better than the Thomas and Yoon-Nelson models at the beginning of the adsorption process. To evaluate its applicability, the continuous flow system based on the monolithic Cry-CSH column was applied for the removal of phosphate from the discharge effluent of the Patong Municipality Wastewater Treatment Plant (Phuket, Thailand), achieving an excellent total adsorption of 94.61%.

Starch Biocryogel for Removal of Methylene Blue by Batch Adsorption.

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.

Portable Colorimetric Hydrogel Test Kits and On-Mobile Digital Image Colorimetry for On-Site Determination of Nutrients in Water.

Portable colorimetric hydrogel test kits are newly developed for the on-site detection of nitrite, nitrate, and phosphate in water. Griess-doped hydrogel was prepared at the bottom of a 1.5 mL plastic tube for nitrite detection, a nitrate reduction film based on zinc powder was placed on the inner lid of a second 1.5 mL plastic tube for use in conjunction with the Griess-doped hydrogel for nitrate detection, and a molybdenum blue-based reagent was entrapped within a poly(vinyl alcohol) hydrogel matrix placed at the bottom of a third 1.5 mL plastic tube to detect phosphate. These test kits are usable with on-mobile digital image colorimetry (DIC) for the on-site determination of nutrients with good analytical performance. The detection limits were 0.02, 0.04, and 0.14 mg L−1 for nitrite, nitrate, and phosphate, respectively, with good accuracy (<4.8% relative error) and precision (<1.85% relative standard deviation). These test kits and on-mobile DIC were used for the on-site determination of nutrients in the Pak Bang and Bang Yai canals, the main canals in Phuket, Thailand. The concentrations of nitrite, nitrate, and phosphate were undetectable to 0.60 mg L−1, undetectable to 2.98 mg L−1, and undetectable to 0.52 mg L−1, respectively.

Plastic/Natural Fiber Composite Based on Recycled Expanded Polystyrene Foam Waste.

A novel reinforced recycled expanded polystyrene (r-EPS) foam/natural fiber composite was successfully developed. EPS was recycled by means of the dissolution method using an accessible commercial mixed organic solvent, while natural fibers, i.e., coconut husk fiber (coir) and banana stem fiber (BSF) were used as reinforcement materials. The treatment of natural fibers with 5% (w/v) sodium hydroxide solution reduces the number of -OH groups and non-cellulose components in the fibers, more so with longer treatments. The natural fibers treated for 6 h showed rough surfaces that provided good adhesion and interlocking with the polymer matrix for mechanical reinforcement. The tensile strength and impact strength of r-EPS foam composites with treated fibers were higher than for non-filled r-EPS foam, whereas their flexural strengths were lower. Thus, this study has demonstrated an alternative way to produce recycled polymer/natural fiber composites via the dissolution method, with promising enhanced mechanical properties.

Greener Monolithic Solid Phase Extraction Biosorbent Based on Calcium Cross-Linked Starch Cryogel Composite Graphene Oxide Nanoparticles for Benzo(a)pyrene Analysis.

Benzo(a)pyrene (BaP) has been recognized as a marker for the detection of carcinogenic polycyclic aromatic hydrocarbons. In this work, a novel monolithic solid-phase extraction (SPE) sorbent based on graphene oxide nanoparticles (GO) in starch-based cryogel composite (GO-Cry) was successfully prepared for BaP analysis. Rice flour and tapioca starch (gel precursors) were gelatinized in limewater (cross-linker) under alkaline conditions before addition of GO (filler) that can increase the ability to extract BaP up to 2.6-fold. BaP analysis had a linear range of 10 to 1000 µgL-1 with good linearity (R2 = 0.9971) and high sensitivity (4.1 ± 0.1 a.u./(µgL-1)). The limit of detection and limit of quantification were 4.21 ± 0.06 and 14.04 ± 0.19 µgL-1, respectively, with excellent precision (0.17 to 2.45%RSD). The accuracy in terms of recovery from spiked samples was in the range of 84 to 110% with no significant difference to a C18 cartridge. GO-Cry can be reproducibly prepared with 2.8%RSD from 4 lots and can be reused at least 10 times, which not only helps reduce the analysis costs (~0.41USD per analysis), but also reduces the resultant waste to the environment.

A novel colorimetric sensor based on modified mesoporous silica nanoparticles for rapid on-site detection of nitrite.

A novel colorimetric sheet based on Griess reagent-doped mesoporous silica nanoparticles was developed for nitrite detection. Griess reagent was adsorbed on long-range ordered hexagonal mesoporous silica nanoparticles and developed ink-bottle pores with some disorder. When the modified nanoparticles were bound using starch to fabricate a thin (~ 313 µm) colorimetric sheet, spherical particles with a rougher surface and some distortion of their mesoporosity were observed. The sheet was used in conjunction with digital image colorimetry (DIC) and provides a wide linear range of 0.05 to 2.50 mg L-1 with a low detection limit (15.0 µg L-1-NO2-, equal to 4.5 µg L-1 NO2--N), good inter-day precision (1.93%RSD), and excellent precision (2.67% relative error). The colorimetric sensors produced from the sheet costs only 0.04 USD each, while the DIC uses a standard smartphone for photographic detection. The method developed offers an easier and cheaper means of conducting rapid on-site determination of nitrite in water with reliable quantitative results. Graphical abstract.

Tetramethylammonium Hydroxide-doped Starch Film as a Colorimetric Sensor for Trinitrotoluene Detection.

A tetramethylammonium hydroxide (TMAH)-doped starch film was developed for trinitrotoluene (TNT) detection. A purple Janowsky anion was obtained from the reaction of TNT with released TMAH. When the film was used in conjunction with digital image colorimetry (DIC), rapid quantitative analysis of TNT was achieved. The Red-Green-Blue (RGB) intensities analyzed from digital photographs of the purple product were used to establish calibration curves for TNT. A wide linear range (2.5 to 50 mgL-1) with good linearity (R2 > 0.99) was achieved for the quantification of TNT. Good precision (1.73 to 3.74%RSD) was obtained for inter-day tests (n = 5). The films were applied to test four post-blast soil samples and two positive results were observed. The concentrations quantified by DIC were in good agreement with spectrophotometry. The film was able to be stored in a freezer for 3 months with <4.3% change in performance.

Portable and selective colorimetric film and digital image colorimetry for detection of iron.

Iron is an important trace element in environmental and biological systems, the development of simple and selective methods for the determination of iron is important. In this work, completely biodegradable tapioca starch was introduced as the substrate to entrap standard chromogenic probes (1,10-phenanthroline) for fabrication of a novel colorimetric sensor for ferrous. A clear plasticized thin film from tapioca starch was fabricated inside a small plastic tube as a portable test kit. A red complex was obtained by exposing the film to a ferrous solution, while no color changes were obtained with various other ions, indicating excellent selectivity. The developed films were applied in conjunction with a digital image colorimetry for quantification of ferrous. Calculated molecular absorption of the red complex showed the widest linear range (0 to 10 mg L-1) with good linearity (R2 < 0.9934) with ferrous concentrations. The developed method provided good inter-day precision (1.75 to 3.97%RSD, 5 days 15 sensors), good accuracy (+2.35% to +4.57% relative error), and low detection limit (0.09 ±â€¯0.01 mg L-1). The concentrations of ferrous ion in soil and water samples quantified by the developed method were not significantly different from atomic absorption spectrophotometry at 95% confidence level. The films were stable for at least three months.