Enhanced adsorption of Pb2+ by the oxygen-containing functional groups enriched activated carbon

Lead is one of the primary pollutants found in water and poses significant toxicity risks to humans; thus, it is necessary to investigate techniques for removing it economically and efficiently. In order to enhance the removal capacity of Pb2+, coconut shell-based activated carbon (AC) was modified with introducing oxygen-containing functional groups (OFGs) via nitric acid (HNO3) or hydrogen peroxide (H2O2) modification in this study. The characterization results show that after oxidation treatment, the content of OFGs increased, and the textural properties of the samples do not change significantly. This indicates that the modification conditions used in this study effectively introduced OFGs while avoiding the adverse effects on physical adsorption ability of AC caused by oxidation treatment. The Pb2+ adsorption capacities of the AC modified with 10 M HNO3 and 30 wt.% H2O2 were 4.26 and 3.64 times that of the pristine AC, respectively. The experimental data can be well fitted using the Langmuir isotherm model and the Elovich kinetic model, suggesting that the adsorption of Pb2+ on AC belongs to single-layer adsorption, and chemical adsorption dominates the adsorption process. In summary, the hydrothermal-assisted HNO3/H2O2-modified coconut shell-based AC shows great potential in efficiently removing Pb2+ from solutions, offering a solution for utilizing coconut shell waste.

Fabrication of Optical Fourier Surface by Multiple-Frequency Vibration Cutting for Structural True Coloration

Optical Fourier surface is a unique patterned optical surface containing the precise sum of sinusoidal waves, each with a well-defined spatial frequency and amplitude. It can manipulate the desired diffracted light field through its Fourier transform, which brings a straightforward mathematical method for designing complex diffractive optics. However, the fabrication techniques typically have the drawbacks of low efficiency, limiting the large-scale industrial application of optical Fourier surfaces. This study presents a powerful approach, the multi-frequency vibration cutting (MFVC), to enable the high-efficiency fabrication of optical Fourier surfaces. A specific optical Fourier surface consisting of arbitrary frequency components of linear gratings has been fabricated on metallic surfaces using MFVC. Due to the capacity of multicomponent gratings in coupling red, green, and blue lights at the same incident angle, the RGB true color has been prepared. The additive and subtractive principles of mixing the three primary colors are demonstrated. The former relies on the light dispersion induced by grating diffraction, while the latter is based on the light absorption induced by the subwavelength grating-coupled surface plasma polarization (SPP). The experimental results of authentic structural true color on the aluminum surface verify the efficacy of MFVC in the fabrication of optical Fourier surfaces.