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Table 2 A summary of common chemical and enzymatic treatment methods for producing (L)CNMs

From: Towards sustainable production and utilization of plant-biomass-based nanomaterials: a review and analysis of recent developments

Methods Chemical Chemical recovery, impact 1 Raw materials CNM type Surface groups Refs.
Concentrated mineral acid hydrolysis Sulfuric acid  −  Bleached wood pulp CNCs [HSO3] [21, 112]
Hydrochloric acid  −  Bleached softwood pulp CNCs None [149]
Phosphoric acid  −  Whatman paper CNCs [PO4] [150]
Sulfuric acid  −  Bleached wood pulp CNCs + CNFs [HSO3] [126, 142]
Sulfuric acid  −  Poplar wood LCNCs [HSO3] [120]
Concentrated dicarboxylic acid hydrolysis Oxalic acid or Maleic acid  +  Bleached wood pulp CNCs + CNFs [COOH] [143, 148]
Oxalic acid  +  Whatman paper CNCs + CNFs [COOH] [151]
Maleic acid  +  Unbleached hardwood pulp LCNCs + LCNFs [COOH] [123, 124]
Acid hydrotrope p-TsOH (aromatic sulfonic acid) 0 Undelignified birch fibers
Wheat straw
LCNFs
LCNFs
None
None
[72]
[44]
Maleic acid  +  Poplar, birch wood
Switchgrass
LCNFs
LCNFs
[COOH]
[COOH]
[45, 121]
[152]
Dilute acid Oxalic acid 0 Bleached wood pulp CNFs None [117]
Oxidation Ammonia persulfate  −  Variety cellulosic materials CNCs [COOH] [130]
Ammonia persulfate  −  Bleached birch pulp CNFs [COOH] [153]
Periodate + chlorite  −  Bleached wood pulp CNFs [COOH] [129]
TEMPO + NaBr + NaClO 0 Bleached wood pulp CNFs [COOH] [140]
TEMPO + NaBr + NaClO  −  Softwood mechanical pulp LCNFs [COOH] [154]
Solvent DES Choline chloride + urea 0 Bleached birch pulp CNFs None [132]
GVL GVL 0 Unbleached GVL pulp LCNFs None [128]
Organosolv Ethanol + SO2 0 Wood LCNCs, LCNFs None [127]
Ionic Liquid [BMIMCI] 0 Cellulose powder CNFs None [155]
[BMIM][HSO4] 0 Bleached wood pulp; microcrystalline cellulose CNCs None [156]
[EMIM][OAc] 0 Wood LCNCs None [157]
Enzymes Endoglucanase  ~  Bleached wood pulp CNFs None [118, 119, 134]
Xylanase  ~  Bleached wood pulp CNFs None [135, 136]
Complex enzymes  ~  Bleached wood pulp CNFs None [137]
  1. 1 − : difficult and negative impact; + : relatively easy and less impact; 0: moderate; ~ : benign and low dosage no need for recovery