Disk I/O and PAGEIOLATCH_XX
PAGEIOLATCH_XX waits are logged by SQL Server when it is waiting for data to be read from the disk. Index maintenance is a notoriously intensive operation and because of this it should be performed at your quietest times to avoid any impact on production.  

You mention you have queries that are causing the same waits. If this is at the same time as the index maintenance then that is not that odd but if it's happening at other times it could be down to memory pressure (not enough room in RAM to store pages so they need to be read from the disk again), large scans or it could even indicate there is a potential problem with your disks. More investigation is needed to rule each of these out.