**4. Conclusions**

The conversion of corncob into reducing sugars was achieved using bamboo-derived carbonaceous magnetic solid acid as the catalyst. The prepared catalysts contained –SO3H, –COOH, and polycyclic aromatic, and the number of H+ sites was from 0.6487 mmol/g to 2.3204 mmol/g. Comparing with the catalysts prepared by dilute alkali and DI water pretreatments, bamboo-derived carbonaceous magnetic solid acid prepared by dilute acid-pretreated bamboo showed better catalytic activity for the production of reducing sugars. The highest reducing sugars yield of 37.17% could be obtained using 0.25% of H2SO4-pretreated bamboo-derived carbonaceous solid acid as catalyst at 120 ◦C for 30 min.

**Author Contributions:** Formal analysis, Y.Z., J.H., and S.S.; Methodology, A.W. and H.L.; Supervision, A.W. and H.L.; Writing—review and editing, Y.Z., J.H. and H.L.

**Funding:** This research was funded by National Natural Science Foundation of China (NO. 31700506), Natural Science Foundation of Guangdong Province, China (NO. 2017A030310550) and Guangdong Province Science and Technology Project (NO. 2016A010104012).

**Conflicts of Interest:** The authors declare no conflict of interest.
