Jem 2100hr transmission electron microscope

A total of 53 sediment and soil samples were collected from a wide range of natural environments across China and Australia (Fig. 2a), including 13 sediment samples that have been described previously [41 (link), 88 ] (for details, see Supplementary Table 1). Each sample was examined for the presence of living MTB by light microscopy using the hanging-drop method [89 (link)]. MTB cells from sediments and peatland soils were enriched magnetically using a “MTB trap” and enriched MTB cells were then subjected to metagenomic analyses, the detailed procedures for which are described elsewhere [45 (link), 90 (link)]. The morphologies of enriched cells were examined using a JEM-2100 HR transmission electron microscope (JEOL, Japan) at 200 kV.

The virus particles were assessed by negative stain and transmission electron microscopy. Briefly, approximately 3–5 µL samples were spotted onto a 400-mesh carbon-coated copper grid, incubated for 1 min, quickly removed and air-dried. Then the grid was stained with 2% phosphotungstic acid (pH 7.4) for 2 min, removed immediately by adsorption to filter paper, washed with a drop of water, and air-dried again. Grids were examined using a JEM2100 (HR) transmission electron microscope (JEOL, Tokyo, Japan) at a magnification setting of 30,000× and an accelerating voltage of 100 kV.

To observe the morphology and structures of our samples, we used Hitachi S-4800 field-emission scanning electron microscope (FE-SEM, Chiyoda, Tokyo, Japan) with an acceleration voltage of 10.0 kV and JEM-2100HR transmission electron microscope operating at 200 kV (TEM, JEOL Ltd., Akishima, Tokyo, Japan). X-Ray diffraction (XRD) data were recorded on Bruker AXS D8 Advance device (Billerica, MA, Cu-Kα λ = 1.5418 Å) working at 40 kV and 40 mA (2θ = 0.02° per step). X-Ray photoelectron spectroscopy (XPS, Thermo Scientific ESCALAB 250Xi spectrometer Al-Kα, Waltham, Massachusetts, USA) was obtained to analyze the composition and existing status of elements. In order to investigate the structures more detailedly, Fourier Transform Infrared spectra (FTIR, Nicolet Avatar 360, Nicolet, Waltham, Massachusetts, USA, KBr pellets) and Raman spectroscopy (LABRAM HR, Horiba, Kyoto, Japan) data were also collected. Thermo Gravimetric Analysis (TGA) was performed on Pysis 1 (PerkinElmer, Waltham, MA, USA) system in air with a heating rate of ∼10 °C min⁻¹. The Mott–Schottky curve measurements were performed in a typical three-electrode electrochemical system (CHI 760e, Chenhua, Shanghai, China) at room temperature using Pt wire as the counter electrode and SCE as the reference electrode.

The TEM images of CNDs solution with a concentration of 0.35 mM were obtained with a JEM-2100HR transmission electron microscope (JEOL, Japan). The CNDs (0.02 g) were fully reacted with H₂O₂ (1.0 mM), and the supernatant was discarded when no more bubbles were generated, dried under vacuum and washed three times with deionized water. The reacted sample (0.01 g) and the original sample (0.01 g) were analyzed by XPS separately. XPS spectra were obtained with a XPS spectrometer (ThermoFisher Nexsa, America). The Raman spectra of CNDs and CNDs + H₂O₂ were recorded by 488 nm laser. Raman spectra were obtained with a Alpha300R Raman spectrometer (Wealtec, Germany).

The ultraviolet–visible light (UV–Vis) absorption spectra were recorded using a UV-1800 spectrophotometer (Shimadzu Co., Kyoto, Japan). The emission spectra were obtained on a Hitachi F-7000 fluorescence spectrophotometer (Hitachi Ltd., Tokyo, Japan). Transmission electron microscopy (TEM) was performed at room temperature using a JEM-2100HR transmission electron microscope (JEOL, Tokyo, Japan) with an accelerating voltage of 200 kV.