Data on a two-dimensional Pd-cellulose with optimized morphology for the effective solar to steam generation

 We share additional XRD identification data of the Pd nanoparticles on the surface of cellulose along with changes in the surface chemistry of cellulose upon treatment (Figure 1). Figure 1ab depicts shows the XRD lines of cellulose and Pd-cellulose. The XRD pattern of cellulose with a dominant (002) peak is indicative of a highly crystalline structure [1]. The (002) peak corresponds to the interplanar spacing between the repeating crystalline units within the cellulose structure. The (101) and (040) peaks are also characteristic of cellulose and correspond to other interplanar spacing in the crystal lattice. Additionally, in the XRD spectrum for Pd-Cellulose (Figure 1b) we detected two peaks representing Pd with the (111) and (200) planes being the most prominent crystal orientations. 

Figure 1c shows deconvoluted XPS spectra results the peaks located at 282.7 eV, 284.8 eV, 286.3 eV, and 287.7 eV could be assigned to specific chemical environments present on the surface of the cellulose [2]. The peak assignment is as follows: (i) The peak at 282.7 eV could be attributed to C-C/C-H groups, such as those present in the cellulose backbone or in any residual lignin or hemicellulose that may be present. (ii) The peak at 284.8 eV corresponds to the C1s transition in the cellulose molecule, and is, therefore, the dominant peak in the spectrum. (iii) The peak at 286.3 eV could be assigned to C-O groups, which are present in various forms in the cellulose structure, such as in hydroxyl groups or in ether linkages. (iv) The peak at 287.7 eV could be attributed to COO groups, which may be present in carboxylic acid or ester groups resulting from cellulose extraction and/or processing. After plasma treatment, we observed the occurrence of an additional peak situated around 289 eV that could be ascribed to oxygen-containing functional groups, such as carbonyl (C=O) and carboxyl (COOH) groups, which have been reported to be formed on cellulose surfaces after plasma treatment in the atmospheric environment, and these groups typically have binding energies in the range of 287-291 eV [2]. 

SEM images of Pd-cellulose synthesized using various precursor loadings and plasma powers are shown in Figure 2. 

SEM images of Pd-cellulose synthesized using the thermal method are shown in Figure 3. From the comparison of SEM pictures, we could conclude that the key difference between these two synthesis processes is the nature of the reduction species, radicals in plasma, and hydroxyl surface functional groups on the surface of cellulose in thermal synthesis. The radicals are in a high concentration in the plasma medium, however, their distribution is random, whilst the hydroxyl radicals are uniformly distributed around the cellulose fiber surface. Therefore, in the case of plasma synthesis, the reduction happens at the site where plasma radicals collide with Pd ion and in thermal synthesis at the adsorption site.

Figure 4 shows the optical properties of the as-synthesized Pd-Cellulose (200 mM and 150-200 W) using UV-Vis-NIR spectrophotometry. 

The evaporation rates of the absorbers synthesized using various precursors concentrations and plasma powers were measured and summarized in Figure 5 and Table 1.