2.1 Preparation of raw materials
Green liquor dregs wastes were supplied by CMPC located in Guaiba/Brazil. This residue and commercial activated carbon (CAC) (PA, Dinâmica) were dried at 50 °C and sieved (100-mesh screen; aperture of 150 µm). Neat PU, CAC/PU and dregs/PU were prepared by the free expansion method using two mixture components (A and B) at a 1:1 NCO/OH ratio and 5% filler content (Delucis et al., 2018). Component A consisted of castor oil (hydroxyl content of 160 mg KOH·g-1), glycerin P.A., dregs/CAC, chain extender (polyethylene glycol), surfactant (Tegostab B804) and distilled water, which was homogenized for 60 s at 1000 rpm under mechanical stirring and was then left to degas for 120 s. Component B is catalyst (Tegoamin DMEA) and a polymeric MDI (Diphenylmethane Diisocyanate), which was added to the Component A and then stirred for 20 s under mechanical agitation. The final mixture was poured into an open mold and left to rise for 24 h. The solid foam was cured at 60°C for 2 h in an oven and post-cured at 65% relative humidity and 20°C for two weeks, as recommended by the literature (Delucis et al., 2018).
2.2 Scanning electron microscopy (SEM)
Surface morphologies of the different materials were obtained by scanning electron microscopy (SEM) (JEOL, JSM 6610LV, Japan). The working voltage was 15 kV and the magnification of 100×.
2.3 X–ray diffraction (DRX)
X–ray diffraction (XRD) patterns were obtained using a diffractometer (Brunker D–8, Germany), provided with a diffracted beam monochromator and Ni filtered CuKα radiation (λ = 1.5406 Å). The voltage was of 40 kV and the intensity of 40 mA. The 2θ angle was scanned between 10° and 60°, and the counting time was of 1.0 s at each angle step (0.02°).
2.4 Fourier-transform infrared spectroscopy (FT-IR)
Chemical groups were obtained with Fourier-transform infrared spectroscopy (FT-IR) using IRPrestige-21 (Shimadzu, Japan) scanning from 500 to 4000 cm-1, 32 scans, transmittance mode, and resolution of 4 cm-1.
2.5 Point of Zero Charge (PZC)
Point of zero charge (PZC) were obtained using the 24 h agitation contact at 50 rpm in initial pH solutions that varied from 1 to 12. The PZC was obtained after plotting the ΔpH (pH final – pH initial) versus initial pH. This methodology was adapted from that described by Farage et al. (2020).
2.6 SARS-CoV-2 inactivated
An inactivated SARS-CoV-2 virus used as a positive control and comes from a clinical isolated in Vero-E6 cell culture (SARS.COV-2 / SP02 / human2020 / Br, GenBank accession number MT126808.1). This virus was kindly provided by Prof. Dr. Edison Luiz Durigon from Department of Microbiology, Institute of Biomedical Sciences, University of São Paulo (USP), Brazil (Dorlass et al., 2020).
2.6.1 Removal of SARS-CoV-2 from the water
10 mg of each adsorbent were properly dried at 37 °C for 2 h. Afterwards, the adsorbent was transferred to a microtube containing 1.5 mL of ultrapure water (free of all RNAse enzymes) and 150 µL of the inactivated SARS-COV-2 viral suspension (2.5 x 106 copies/mL) was then added, which was followed by incubation with shaking at 200 rpm and 28 °C for 24 h. Subsequently, both supernatant and adsorbent were removed and placed into another microtube, and the viral RNA was then extracted.
2.6.2 RNA extraction
The RNA was extracted from both supernatant and studied adsorbents using a MagMax™ Core Nucleic Acid Purification kit (Thermo Fisher Scientific, Waltham, MA, USA). The extracted RNA was quantified by Nano Drop® (Thermo Scientific, Waltham, MA, USA). A concentration of approximately 10 ng of RNA was used to perform the RT-qPCR detection.
The primer and probe used in PCR reactions was designed according to the sequences published by the Centers for Disease Control and Prevention (CDC, 2020). Briefly, a reaction of 25 μL of final volume was used, with the following volumes added to the 1× concentrated master mix: 5 μL of sample RNA, 12.5 μL of 2× reaction buffer, 1 μL of SuperscriptTM III One-Step with PlatinumTM Taq DNA Polymerase (Invitrogen, Darmstadt, Germany), 0.4 mM of each dNTP, 0.4 μL of a 50 mM MgSO4 solution (Invitrogen), 1 μg of non-acetylated bovine albumin (Roche), 10 μM of each primer 2019-nCoVN1-F2019-nCoV N1 (5’GACCCCAAAATCAGCGAAAT3’), 2019-nCoVN1-R2019-nCoV N1 (5’TCTGGTTACTGCCAGTTGAATCTG3’), 2019-nCoVN1-P2019-nCoV N1 probe (5’-FAM – ACCCCGCATTACGTTTGGTGGACC– BBQ 3’), and DEPC water. The reaction occurred in StepOneTM Real-Time PCR System (Thermo Fisher Scientific, Waltham, MA, USA) in the following cycling: 55°C for 10 min for reverse transcription, followed by 95°C for 3 min and 40 cycles of 95°C for 15 s, 58°C for 30 s.
2.6.4 Statistical analysis
Data were expressed as mean ± standard deviation for duplicates for each experimental point. Data were analyzed by using one-way analysis of variance (ANOVA) followed by Bonferroni's multiple comparison tests adjusted for a significance level of 5%.