Electronic Supplementary Information Upcycling agricultural waste into membranes: from date seed biomass to oil and solvent-resistant nanofiltration

Membranes hold a great promise for replacing energy-intensive separations across various industrial sectors. However, membrane production heavily relies on petrochemical-based raw materials; the need for greener membranes is a challenge...


Chemical analysis of the membranes
. EDX elemental analysis of the prepared membranes. The y-axis represents the count of elements, and the x-axis represents the energy in keV.

Date seed composition
The NREL 1 protocol was used for quantifying cellulose, hemicellulose, and lignin in date seeds in conjunction with other protocols, as stated below. 2

Determination of extractives
A sample containing 2 g of raw date seeds was extracted using a Soxhlet extractor. The first extraction employed a 150-mL ethanol-benzene (1:2) mixture for 4 h. The second extraction employed dichloromethane for another 4 h. Solvents were evaporated slowly until a constant weight was obtained for the extracted oil residue. The weight percent (%) of extractives was calculated based on the original mass of the dried date seed sample.

Determination of holocellulose
The extractive-free dry sample was transferred into a 250-mL Erlenmeyer flask. Deionized (DI) water (160 mL), glacial acetic acid (0.5 mL), and sodium chloride (1.5 g) were added to the flask, and the temperature was maintained at 70 °C for 1 h under continuous stirring. Then, glacial acetic acid (0.5 mL) and sodium chloride (1.5 g) were added to the flask and stirred for another 1 h. The procedure was repeated twice (i.e., third and fourth addition of reagents). The reaction flask was cooled in an ice bath (~8 °C); then, holocellulose was filtered using a filtration thimble, washed with acetone, extracted in ethanol using the Soxhlet extractor for 2 h, washed with DI water, and dried in an oven at 110 °C until a constant weight was obtained.

Determination of lignin
The extractive-free dry sample was transferred into a 50-mL beaker with 5 mL of DI water. Then, 15 mL of 97% sulfuric acid (H2SO4) was added gradually to the sample in an ice bath maintained at ~8 °C to obtain a 72.8% H2SO4 solution. The sample was mixed using a magnetic stirrer for 2 h and then transferred slowly into a 1-L beaker containing 485 mL of DI water (3% H2SO4). The sample in the beaker was continuously stirred for 4 h. The solution was left overnight to settle and precipitate lignin, S13 which was collected via vacuum filtration and dried at 110 °C until a constant weight was obtained.
The weight (%) was calculated on the basis of the original weight of the date seed sample.

Determination of lignin
The extractive-free and lignin-free holocellulose sample was treated to determine the content of cellulose. The holocellulose was transferred into a 100-mL beaker, and 25 mL of 17.5% sodium hydroxide was added gradually with occasional stirring using an overhead stirrer for 45 min. Thereafter, 33 mL of DI water was added to reach the final a concentration of 7.5% NaOH. Then, the solution was filtered using a vacuum filtration apparatus, and the cellulose residue was washed twice with DI water.
Next, 15 mL of 10% acetic acid was added to the cellulose residue for ~10 min and then washed with DI water (250 mL) until a neutral pH was achieved. Finally, the sample was dried overnight in an oven at 110 °C. The weight (%) of cellulose was calculated on the basis of original dried date seed sample.

Membrane performance
Swelling can be investigated using various techniques with different terminologies in different fields.
However, herein, an increase in sample volume due to solvent contact is taken as an estimate measure for swelling using the lengths of the dry and wet samples (swelling ratio) as it is most widely used in the membrane science literature. 3 Moreover, the weight variations of the sample before and after soaking in the solvent are reported as solvent uptake. The degree of swelling has been correlated with the structural and surface properties of the sample or solute, such as the index of crystallinity, degree of polymerization, porosity, and the structure of pores, as well as solvent properties. The dissolution is defined as the transition from a two-phase system (e.g., solute and solvent) to a one-phase system in which the solute is completely disintegrated. 4    The increased viscosity of the dope solution (approx. 57%) elucidates the higher solvation of the date seed components after water-ethanol treatment compared with that of the untreated date seeds ( Table  S8). 1 Pieces (20-30 mg) of pristine date seed membrane (M 10 ) were dried using an incubator at 400 rpm at 50 ℃ for 24 h and then placed in a vacuum desiccator for 24 h. Thereafter, the samples were placed in 15 mL of acetone, replaced 3 times a day. Finally, the samples were taken out and dried via the same protocol (using incubator and desiccator for 24 h). The weights of the samples were measured before and after the acetone treatment