Litesizer 500 instrument

A Wyatt DynaPro NanoStar DLS instrument was used to measure the NP size distributions. After equilibration for 1 h at room temperature, the solution was diluted 5-fold before transferring to a disposable microcuvette for measurement. The hydrodynamic diameters of the AuNPs were measured using the regularization fit functionality of the DYNAMICS software. For each measurement (with or without PEG), the average value of three independently prepared samples is reported and the uncertainty is calculated as the standard error of the mean. Zeta potential measurements were performed on an Anton Paar Litesizer 500 instrument using Kalliope software.

The nanoparticle dispersions were subjected to DLS using a Litesizer 500 instrument (Anton Paar, Graz, Austria) to determine nanoparticle diameters, size distributions, and zeta potential. This instrument is equipped with a semiconductor laser diode at 40 mW output power operating at 658 nm. Dispersions were loaded into the cuvette and equilibrated at 25 °C for 30 s beforehand. Sixty runs were then made per measurement, following these conditions. The dispersant was water (viscosity: 0.89 mPa·s; refractive index: 1.33). Backscattered light was detected at 90°, and the intensity-average hydrodynamic diameter was calculated using the Stokes–Einstein equation. All data were processed using Kalispell Anton Paar Software (v. 4.82.890)and Microsoft Excel (v. 2308). Three independent experiments were carried out, with triplicate measurements performed for each sample. A Zeiss Merlin VP Compact field emission gun SEM (ZEISS Group, Oberkochen, Germany) was also employed to analyse nanoparticle shape and size. Approximately 10,000 nanoparticles per sample were analysed using our unique method, exploiting the coffee-ring effect that aids in the size-based classification of nanoparticles [35 (link)]. The nanoparticles were left to dry and distributed on a silicon wafer according to the coffee-ring effect. Three independent experiments were conducted, each with triplicate measurements.

Fourier transform infrared (FT-IR) spectra were recorded in transmission mode on a Thermo Scientific Nicolet iS5 FT-IR spectrometer with the KBr method. X-ray photoelectron spectroscopy (XPS) was measured with a Thermo Fisher Scientific ESCALAB 250Xi instrument. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) were performed on the FEI Tecnai G2 20 S-TWIN with a LaB₆ cathode operated at 200 kV. UV-vis absorption spectra were acquired on a CARY 50 spectrophotometer. Powder X-ray diffraction (XRD) measurements were performed on a Philips X'Pert MPD Pro X-ray diffractometer at a scanning rate of 4° min⁻¹ in the 2θ range from 10° to 80° (Cu Kα radiation, λ = 0.15406 nm). ζ-Potential measurements were carried out on an Anton Paar Litesizer™ 500 instrument. Upconversion luminescence (UCL) emission spectra were obtained on a fiber-coupled spectrometer (Ocean HDX, Ocean Optics) with an external 980 nm continuous-wave (CW) laser (0–5 W, Roithner Lasertechnik GmbH) at room temperature (RT). Quartz cuvettes (0.7 mL, 10 mm × 2 mm light path) were used for UV-vis absorption and UCL measurements.

The average particle size of raw and nano-scale kraft lignin was measured via dynamic light scattering (DLS) on a Litesizer 500 instrument (Anton Paar, Graz, Austria). The powders were dispersed and ultrasonicated in deionized (DI) water at a concentration of 100 ppm for 5 min prior to measurement. The hydrodynamic diameter was around 2.7 μm (polydispersity index, PDI = 28%) for raw lignin and 651 nm (PDI = 23%) for nanolignin. Particle size distribution curves for both samples are presented in Figure S1a. The thermal stability was evaluated with TGA (Figure S1b), where it was confirmed that both L and NL are thermally stable upon heating in air up to 180 °C.

Total phenolics were determined by the Folin–Ciocalteu method according to the procedure reported in [26 (link)]. The results were expressed as gallic acid equivalents (GAE) using a calibration curve obtained with gallic acid standards.
Spectrophotometric measurements were made with a double-beam UV-Vis spectrophotometer (mod. UV-2700, Shimadzu, Kyoto, Japan).
An X’Pert PRO diffractometer (Philips, Eindhoven, The Netherlands) was used for XRD measurements. The instrument was operated at 40 kV and 30 mA with Cu Kα radiation (λ = 1.5406 Å). The 2θ angle was varied from 20° to 80°. The step size was 0.04° and the counting time was 20 s per step.
Nanoparticle size and zeta potential were measured using a Litesizer™ 500 instrument (Anton Paar, Graz, Austria).
Transmission electron microscopy (TEM) images were obtained with a Zeiss EM10 instrument (Carl Zeiss, Thornwood, NY, USA) operated at 60 kV. Samples were prepared by placing a drop of the nanoparticle solution onto a standard carbon-coated copper grid. Images were analyzed by the ImageJ software (ImageJ, National Institutes of Health, Bethesda, MD, USA).

The average particle size of raw lignin and nanolignin was measured using dynamic light scattering (DLS) on a Litesizer 500 instrument (Anton Paar, Graz, Austria). The powders were dispersed in water at a concentration of 100 ppm via ultrasonication for 5 min prior to measurement. The hydrodynamic diameter was 2.38 μm (polydispersity index, PDI = 0.29) for raw lignin and 524 nm (PDI = 0.16) for nanolignin. Particle size distribution curves of both samples are presented in Figure S1.