Equinox 55

Fourier-transform infrared (FT-IR) spectroscopy in the form of ATR-FTIR was also employed to verify the chemical structure of the synthesized copolymer. The mid-infrared measurement was conducted at room temperature, in the spectral range of 5000–550 cm⁻¹, using a Fourier transform instrument (Bruker Equinox 55, Bruker Optics GmbH, Ettlingen, Germany) equipped with a single bounce attenuated total reflectance (ATR) diamond accessory (Dura-Samp1IR II by SensIR Technologies, Chapel Hill, NC, USA). The polymer sample was measured in the solid state and the spectrum was recorded after 64 scans with a resolution of 4 cm⁻¹.
ATR-FTIR spectral peaks of P(SMA-co-OEGMA), v (cm⁻¹), (s: stretching, b: bending): (CH₂): 2922 (s), 2854 (s) and 1454 (b), (C=O): 1728 (s), (C-O-C): 1105 (s).

Fourier-transform infrared spectroscopy (FTIR) measurements were performed in order to verify the chemical structure of the P(DMAEMA-co-OEGMA) copolymers and particularly to certify the modification of the tertiary amines of the precursor copolymers to quaternized ammonium salts. The measurements were implemented at room temperature in the range of 5000–550 cm⁻¹ using a Fourier transform instrument (Bruker Equinox 55, Bruker Optics GmbH, Ettlingen, Germany) equipped with a single bounce attenuated total reflectance (ATR) diamond accessory (Dura-Samp1IR II by SensIR Technologies, Chapel Hill, NC, USA). The copolymer samples were analyzed in the solid state and the spectra were recorded after 64 scans with a resolution of 4 cm⁻¹.
ATR-FTIR spectral peaks of P(DMAEMA-co-OEGMA), v (cm⁻¹), (s: stretching, b: bending): (CH₂): 2922 (s), 2854 (s) and 1458 (b), (-N(CH₃)₂): 2821 (s) and 2765 (s), (C=O): 1722 (s), (C-N): 1145 (s), (-O=C-O-C): 1100 (s).
ATR-FTIR spectral peaks of P(QDMAEMA-co-OEGMA), v (cm⁻¹): (O-H) (internal moisture) 3467 (s) and 1640 (b), (C-N(CH₃)₃⁺): 3005 (s), 1474 (s) and 950 (s), (CH₂): 2871 (s) and 1458 (b), (C=O): 1722, (C-N): 1145 (s), (-O=C-O-C): 1100 (s).

Scanning electron microscopy (SEM) analyses were conducted to study the structure of acid-leaching- and water-leaching-pretreated RH samples at the micro level. The dried RH samples were coated with gold in a sputter coater. The SEM experiment was performed on a PHILIPS ESEM XL-30 (FEI, Hillsboro, OR, USA) operating at 20 kV with a 15 mm working distance.
The functional groups in the RH samples were determined using an FTIR equipment BRUKER EQUINOX 55 (Bruker, Karlsruhe, Germany). The spectra were recorded with 32 scans at a resolution of 4 cm⁻¹ in the range of 4000–400 cm⁻¹.