Nanocelluloses including cellulose nanocrystals and cellulose nanofibers have gained increasing attention and interest from researchers and the industry because of their extraordinary properties and wide application potentials in emulsions and foams, biomedical devices, electronics and sensors, high-viscosity fluids and polymer composites. However, green, fast and low-waste production of cellulose nanocrystals and cellulose nanofibers is still challenging. In this work, the integrated and high-yield production of nanocelluloses was achieved by lignin-based solid acid catalysis and dilute sulfuric acid hydrolysis pretreatment followed by additional homogenization process. Firstly, a low-cost, eco-friendly, and efficient lignin-based solid acid catalyst was used for catalytic transformation of cellulose into short rod-like cellulose nanofibers and platform chemicals. The lignin-based solid acid catalyst was synthesized via a facile carbonization-sulfonation process by using lignin as the carbon source which was separated from enzymatic hydrolyzed residues, a waste from cellulosic ethanol industry. Platform chemicals (including glucose, fructose, formic acid, levulinic acid, and 5-HMF) can be obtained after as-prepared lignin-based solid acid catalytic cellulose hydrolysis pretreatment, and short rod-like cellulose nanofibers were obtained followed by homogenization with large crystallinity index of 82 % and small aspect ratio of 10 ~ 28. Furthermore, lignin-based solid acid catalyst can be recycled and reused. After five successive cycles, the yield of cellulose nanofibers, glucose, and formic acid reached up to 90.8 %, 3.9 %, and 2.1 %, respectively. Secondly, a time-saving and low-cost chemi-mechanical method was proposed to prepare cellulose nanocrystals and cellulose nanofibers by dilute sulfuric acid hydrolysis pretreatment and further homogenization. After the 0.3 wt% sulfuric acid pretreatment at 160 ^oC for 2 h, the yield of cellulose nanocrystals reached to 15.78 %, and the diameter and length distribution of the obtained cellulose nanocrystals were 16 ~ 45 nm and 150 ~ 600 nm, respectively. After further homogenization of unhydrolyzed cellulose residues, a high cellulose nanofibers yield of 69.11 % can be obtained. Besides, the thermostability of cellulose nanocrystals prepared by 0.3 wt% sulfuric acid pretreatment was more superior to that of cellulose nanocrystals manufactured by 64 wt% sulfuric acid. Last but not least, this work provides two novel, low-cost, and promising strategies for efficient preparation of nanocelluloses, and they hold great potential in functional additive, biomedical, nanocomposite, and electronic applications.

Nanocellulose; Pretreatment methods; Lignin-based solid acid; Dilute sulfuric acid;