The vC-O of lactonic system is assigned at 1350 [cm.sup.-1].
The characteristic peak derived from lactonic carbonyl as a result of intramolecular hydrogen bond appears to have moved down at 1637 [cm.sup.-1].
at P = 0.05) Biochar Carboxylic Lactonic
Phenolic Total groups Canola straw 12.1b 32.2d 143b 187b Wheat straw 11.5c 36.5c 116d 164d Rice straw 9.0d 24.1f 106e 139e Rice chaff 13.4a 21.28 87f 122f Corn straw 4.1f 37.2b 81g 122f Soybean straw 6.4e 27.5e 139c 173c Peanut straw 6.4e 36.8b 160a 203a Faba bean straw 1.1h 15.6h 39i 55i Pea straw 0.5i 24.1f 49h 73g Mungbean straw 2.lg 38.8a 26j 67h Table 5.
pH and free, lactonic and total acidities were determined using 10 g of honey dissolved in 75 ml of deionised water.
During heating and storage, significant increases in the free, lactonic and total acidities were detected, especially from nine months' storage (Tables 2-4).
The structure of 3 was confirmed by the IR spectrum which exhibited strong absorption bands at 3200, 3281, 1664, and 1610 [cm.sup.-1] corresponding to [v.sub.NH], [v.sub.C=O], and [v.sub.C=N], respectively and lacked a band corresponding to lactonic
carbonyl group and also the presence of acidic hydrogen in the [sup.1]H-NMR spectrum at [delta] 12.38.
Oxygenated acidic and basic functional groups (mean [+ or -] s.e., [mmol.sub.c]/g C) of biochars, after removing soluble salts and carbonates, as determined by Boehm titrations Biochar treatment Carboxyl Carboxyl + lactonic
+ phenolic E.
Solid Surface area Carboxylic groups Phenolic groups ([m.sup.2][g.sup.-1]) (mmol[g.sup.-1]) (mmol[g.sup.-1]) CC 130 0.13 0.23 CCox3 122 0.26 0.16 CCox6 115 0.38 0.17 CCox9 110 0.46 0.42 Solid Lactonic
groups Total acidity Total basicity (mmol[g.sup.-1]) (mmol[g.sup.-1]) (mmol[g.sup.-1]) CC 0.10 0.46 0.28 CCox3 0.15 0.57 0.12 CCox6 0.20 0.75 0.10 CCox9 0.38 1.26 0.07
The lower pH and PZC could be attributed to the presence of acidic functional groups in the form of lactonic
phenolic and carboxylic functional groups on the surface of activated carbon.
The number and type of acidic sites were calculated by considering that NaOH neutralizes carboxylic, lactonic
, and phonetic groups.